$299 Gibson tube amp - Made in USA!

The difference to my ears was quite apparent and I see no reason to go back to the original circuit. specialty guitars did advise to make the mods permanent if they were liked - dunno why .... :?:

I'm gonna add the NFB (once I know for sure exactly where the 47k resistor goes) and see how that sounds. If need be, the NFB can easily be wired in with a mini switch on the chassis bottom to allow the use of both modes.

Maybe use a 50k pot to dial it in?

The difference to my ears was quite apparent and I see no reason to go back to the original circuit. specialty guitars did advise to make the mods permanent if they were liked - dunno why .... :?:

The only reason why is that having half connect components and superfluous parts running about can make the circuit unstable and cause parasitic oscillations and noise. It's not imperative that the components be removed, just recommended. And even if removed, those parts or new parts, can be reinstalled to reverse the mods.

You want to go to pin 8 on the 12AX7 with the 47k from the speaker output.

I know my picture is lame.

http://www.specialtyguitars.com/images/ebay/nfb.jpg

That schematic is correct in layout, though it's numbered differently than I'm used to seeing.

You want to put a resistor from the cathode of the driver side of the 12AX7 tube to the speaker for a negative feedback loop, as that schematic shows, just don't count on the numbering scheme to match the socket in your amp.

BTW, I'm not an expert, maybe specialty guitars will chime in and clarify.

On this current amp, it's pin 8 on the 12AX7.

I'll go back over this thread and see what you guys think of the various mods. I have the problem that almost all variations and combinations of variations sound good, so it's hard to decide.

I figured the 1m resistor in parallel with the 22pF cap had to go when I first saw the schematic for these amps, before I even ordered mine

Same here. when I saw that on the scheme I went "wtf?"

Gerald Weber mentioned that Gibson amps almost always had some sort of "remedial tone shaping circuitry" and I think that bass cut/treble pass filter would clearly fall under that description!

We need to get all these amps, stock and modded, and all the owners into one room for a giant comparison!

I mentioned to someone else, that although I like the stock speaker, I won't rest easy until I've heard it with an 8" alnico magnet speaker.

Here's where I'm at with it, and I'd appreciate hearing all the feedback from others who are trying these mods.

1. Removed the bass cut/high pass filter. Removed the 22pF and the 1meg and replaced with a straight wire. To my ears, this is a keeper, no matter what.

2. Installed a 47K negative feedback resistor. This tamed the high end, so I...

3. Installed a brighter ribbed cone 8" speaker. In this case, the one I had on hand that is broken in is a Kendrick, but most any brighter sounding ribbed speaker would work like Weber's Sig 8S or a Jensen Ri.

4. At this point, I can't decide if I want the 1st stage 25uF bypass cap in our out. Both ways sound really sweet, just different.

5. Installed a NOS Tungsram 12AX7 I didn't know I had.

And that's it so far.

IMO this thing sounded great out of the box, but is a real head turner now.

I'm kind of pissed, it now sounds much better than my 5F1 which was my living room "pride and joy". (maybe it's just time for a new 6V6...)

I agree with Rob, that the amp is just fine out of the box, and is a real winner for a new tube amp at that price.

I believe I was wrong about the cab being press board. It's not as heavy I seemed to think originally. (it was late)

I suppose one could try different EL84s, but the JJ sounds very nice. I'm not going to bother.

EDIT: I forgot. I also took the 22pF cap, and installed it across the hot and the wiper of the volume pot. This acts as a treble bypass to keep the treble there when the volume is turned down low. It's the same thing the 47uF cap in a Deluxe Reverb on the vibrato channel volume pot is doing. This keeps the treble there and a little "zingy", when the volume is turned down, and is in IMO, what Gibson should have done in the first place instead of that lame low cut filter.

On step 2, you may or may not want to do this, and you may want to try different resistor values. The way it is from the factory with no negative feedback (NFB) is raw, gainy and zippy, which is very cool. The NFB, tames it down and evens the frequency response. A higher value resistor will give it less NFB, so you can experiment and decide.

Maybe use a 50k pot to dial it in?

You could install a 250K or 500K pot, and or a switch, or even a no-load pot in place of both.

specialty -

Is there a reason why you mentioned earlier to completely remove the 1m resistor/22pf cap instead of leaving the jumper in? Ditto's for completely removing the 25uf bypass cap ... ?

He mentioned concern over parasitic noise.

You could always add switches for them.

The amp could have a power switch, volume control and a row of mini-switches that you can't remember the purpose of! :lol:

specialty -

Is there a reason why you mentioned earlier to completely remove the 1m resistor/22pf cap instead of leaving the jumper in? Ditto's for completely removing the 25uf bypass cap ... ?

The only reason why is that having half connect components and superfluous parts running about can make the circuit unstable and cause parasitic oscillations and noise. It's not imperative that the components be removed, just recommended. And even if removed, those parts or new parts, can be reinstalled to reverse the mods.

Red 57 is right. You could add a switch to switch the 25uF cap in and out of circuit. In fact, this is exactly what the "FAT" and "boost" switches are doing on Blues Jr.s and many other amps.

He mentioned concern over parasitic noise.

You could always add switches for them.

The amp could have a power switch, volume control and a row of mini-switches that you can't remember the purpose of! :lol:

Sure thing! You could turn this poor little amp into a hellish nightmare of switches, knobs, pull-chords, rip-chords, knee levers, trap doors, whistles, flashing LEDs, stealth cloaking, Ronco Veggimatics, and secret compartmants. Or just set it up to sound sweet and play it! :smile:

Sure thing! You could turn this poor little amp into a hellish nightmare of switches, knobs, pull-chords, rip-chords, knee levers, trap doors, whistles, flashing LEDs, stealth cloaking, Ronco Veggimatics, and secret compartmants. Or just set it up to sound sweet and play it! :smile:

That's exactly what I've been looking for! (slaps forehead) Do you have a schematic?

That's exactly what I've been looking for! (slaps forehead) Do you have a schematic?

Is that with, or without GPS, and the full body harness so you can strap it to your chest while jogging?

That's exactly what I've been looking for! (slaps forehead)...

http://i235.photobucket.com/albums/ee231/big_lug/thwap.gif?t=1204840100

There you go Blues.

Personally, I'd prefer to tweak the GA-5 tone/gain to my liking as a near set-and-forget kinda deal when it's fed by single coil pup guitars, and use the amp's vol pot and guitar's vol/tone pots as tonal/volume fine tuners. No other switches, dials or idiot lights wanted or needed. :mrgreen: YMMV.

If you want to add some "beef" to the tone, jumper across the the 22pF cap and 1 meg resistor as I mentioned before, shown in the photo. It's easy to do and can be reversed easily. This added some serious balls to it playing my Tele,

Just so I get ya (one more time for the guys in the back of the room), you simply jumped that wire across those lugs and didn't desolder or snip the cap or resistor?

Thanks for the info, it'll be fun, mine comes tomorrow via ups.

Well . . . .

I pulled BOTH metal screens from mine - front and back - between the two maybe 70 staples - and a good pound of metal. Yanked the "cord box" too.

Put it all back together and am very happy with the result.

I can hear a difference - All in my mind?

Don't know for sure but when you get a load of the grill you will understand why I suspect I am hearing it right.

And it suggests why they are so deeply discounted: the metal add-ons and box took a 600-700 dollar amp and so bogged it down as to make it unsellable at that approaching boutique price.

Believe me, the front metal grill is not to be believed!

And then once the commitment was made to crank them out that way there was no going back - i.e.', they couldn't pull the grills like I did and try to sell them as is -

So buy 'em cheap and strip 'em!

Pics coming within the hour.

Just so I get ya (one more time for the guys in the back of the room), you simply jumped that wire across those lugs and didn't desolder or snip the cap or resistor?

Thanks for the info, it'll be fun, mine comes tomorrow via ups.

Yes, to start with. But I added later that it is best to remove them if you decide this is what you want, for stability reasons.

That mod seems to be the way to go no matter what. The other mods will depend on each individual's taste.

I want to add though, that the reason they probably installed this bass filter was to keep the tone from "rolling" when the amp is cranked up. Stripping out bass tends to keep that from happening, but makes the amp sound thin and wimpy otherwise.

Those who have played tweed amps cranked have experienced "rolling". Where the sound seems to go "WheeeshuuuWeeeshuuuWheeeshuuu..." when you hit a full chord and let it sustain.

It seems to me, that Gibson created this amp, and Fender the Champ 600 Ri to be little distortion monsters. Which is OK, but instead of going for "fizzy kid's stuff", they could have made them "adult amplifiers" with less trouble and expense. Fortunately, everything can be modified to most everyone's liking.

How is the GA5 Voiced is it like a marshall or Fender or a blend of the two sounds

I'll be pulling the metal grills and cord box before I do any other mods. I think it's the logical way to go.

Also, I'm kind of stuck doing just that for now because my industrial grade Weller WES51 soldering station is on the fritz! It needs a new circuit board!

This is really bad timing for my favorite tool to let me down.

I have a 15 watt Radio Shack iron as a backup. That might get me by for a couple of weeks.

Here is the front baffle removed from amp without the speaker showing metal grill from the 9465interior.

Here is the grill from the other side with the grill cloth peeled back:9466

Note that the heavy metal grill is inset into the wooden baffle and is glued as well as stapled. Note as well that it covers the entire front of the baffle, not just the speaker hole.

Here is the front metal grill removed from the baffle:9467

Here are the two metal baffles and some of the staples:9468

The two grills combined weight has got to exceed 2 pounds IMHO.

Here is the front baffle removed from amp without the speaker showing metal grill from the interior.

Is that plywood I'm looking at?

Is that plywood I'm looking at?

Yes.

Here are the two metal baffles and some of the staples:9468

The two grills combined weight has got to exceed 2 pounds IMHO.

Damn, that's where the weight was coming from, that made me think the cab was press board.

I have seen pictures on the 'net of the amp - as in the MF add- and you can see a speaker behind the cloth. That of course could be photo shop -

but I have seen actual new model GA-5's - pre-rear grill and box goofiness -on ebay where the grill cloth was similarly revealing.

I could not see my speaker - not even the outline - not even today when I took it outside! I knew then that the metal grill was going to be heavy duty.

The fact that I have seen pics in which I could see the speaker leads me to believe that the heavy front grill was added with the dopey back grill and cord box. Once that was done, a very fine Made in USA tube amp had been so screwed up that the heavy discount followed - to my - and our - profit.

A tip or two on a fast down and dirty way to remove the front metal grate:

Remove rear baffle. Remove it's metal grate while you're at it. Those staples in my case came out with a pair of needle nose pliers. The rare staple piece that broke off and remained in the baffle I hammered in.

Knocked the box off with a blow from a hammer to a well placed screw driver. Used pliers to pull the remaining brads. Pounded in the bits that broke off.

Pulled the chassis - literally. Remove the rear screws - one left one right - and pull chassis out of slots in wood. Marvel at well built and laid out board and amp components. This is a nice amp!

Unscrew speaker baffle and remove out of rear of cabinet.

Remove speaker from baffle.

Remove grill cloth staples from three edges of baffle board.

Attack grate staples - I used a small screw driver to get staples started then pulled them with pliers. Be careful the screw driver doesn't slip and stab you! I worked up a sweat on those many staples.

Once I pulled the metal grate, I carefully placed the grill cloth back - and screwed the baffle tight back into the cabinet w/o restapling the three sides - I know, I'm trash - but I figure I'm not Gibson or Fender so I don't care if the cloth sags in a month or a year or whatever - I have no fear of customer complaints - so I don't need a zillion staples - and I damn sure don't need that stupid metal grate business!!! Screwed in tight that grill looks factory fresh with staples on one edge only. There is so much "cabinet coverage" of the grill I suspect it will stay looking just fine.

Anyway, glad I did it.

Here is a pic of a pre-rear grate GA-5 - notice how you can easily 9470see the speaker through the front grill:

How is the GA5 Voiced is it like a marshall or Fender or a blend of the two sounds

I was thinking kind of Vox - like when clean, and I'm not sure when dirty. Maybe others will chime in.

How is the GA5 Voiced is it like a marshall or Fender or a blend of the two sounds

I'm not sure how to describe it. I've never considered a Champ to sound like a full size Fender amp (tweed or blackface)!
I think it sounds more like a Champ than anything else.

Here is the front baffle removed from amp without the speaker showing metal grill from the 9465interior.

Thanks for all of this. I was planning to attack this project this weeekend. It's nice to see how it all looks.

This may well be the best new tube amp buy of the new millennium.

Just out of curiosity, rather than go to the trouble of removing the rear grill, why not just leave the back off? Any reason other than cosmetic? Mine seems to sound better without the back.

maybe someone could post some sound samples pre and post mod?

Do you guys think the metal grate in the front makes that much of a difference in sound? My 2x10 cab is a Hartke bass cab and it has a metal grate. Didn't think it made that much of a difference in sound.

My first GA-5 is getting the full monty of circuit, speaker and cab mods, the second remains perfectly box stock - this affords some viable sonic A/B testing which I'll carefully record with a Zoom H2 and share on this thread.

I don't think it'll matter much at all if any or all of the grilles are removed - dittos for the removing the entire rear panel.

CIRCUIT (as of 3/7)
* 1m resistor and 22pf cap removed and jumpered
* 1st stage 25uf cap lifted
* 47k NFB added
* 1/4" external 8 ohm speaker jack added
* ground buss rewiring??? - more on this due from specialty

SPEAKER
* Weber 8F150

CAB
* remove the power cord box
* remove the rear grille
* rebaffle with 1/2" birch ply and cane grille

Sidney Vicious seems to think so.

The problem with this grill is that it's so dense. I would think that it would make some difference. It would be different if the amp was voiced with the grill in place. I believe it was an afterthought with these amps.

Besides that, I'm a bit of a purist and don't like extra crap that doesn't belong there and bought this amp to mod and tweak anyway.

IMO, the rear grille is there for corporate protection, and the front grille insures a no-sag cloth front that's "poke proof". In terms of sonics, I still don't think the grilles will much matter, and with the stage of mods I've already done to GA-5 #1 it'd by hard to tell the difference with my stock GA-5 #2. The cane grille I'll be using will be tight as a drum and nearly as "poke proof" while allowing for quite large weave holes for the sound waves to escape.

http://img.photobucket.com/albums/v82/rfdee/cabs/w7.jpg

Just pull mine outa the box, cute thing. Sounds pretty dang good w/ the volume at 5, it does get a little raspy on the top end but not too horrible.

For me it's not a gig amp but it's a fine workbench/utility amp, I've been using a Fender mini bassman (the old yellow plastic one) which will tell you that you've got a good circuit, but that's all, this will be a real improvement.

I'll take it apart and try some of the mods mentioned when I get time, but I'm happy w/ the Gibby.

I believe the rear grill is there to make it certified CE to be sold in Europe. I believe they require that a grill or some other method be used so that there is no way that anyone could stick their hand anywhere and get burned by the tubes.

As far as that weird cord box, I have no idea.

I'm guessing the speaker grill is to keep "little Billy" from sticking his foot or something else through the speaker.

It does all seem a bit much, but such is life in a time when everyone must be protected from themselves. I wonder how many deaths and injuries occurred to guitar players in the 30s 40s 50s 60s and 70s before these modern safety features were required? Sure a lot of Vox amps caught on fire, but that's because they didn't have enough ventilation, because they were...over-enclosed.

I am the first to admit that I may be hearing things with regard to the difference in the sound of the amp without the front metal grate - in fact I was the first to admit it in my original grate-removal post. :lol:

But having said that, I think my ears and mind are not fooling me - that grate would deflect a poke from a thown cue stick! Its as though it were designed to protect something much more irreplacable than a Weber Sig speaker . . . .

I have several vintage Fender amps - as do many of us - that have nothing but a grill cloth protecting the speaker from the world. For whatever reason, Gibson decided that grill cloth is not enough.

I have got to believe that at some point a grate of this sort has a deliterious (sp?) effect on the ability of the sound to escape.

The rear grate is less important - I removed it so that I can put the cord in and out more easily.

I believe the evidence indicates that heavy front metal grate was a late "improvement" to the amp's design - removing it in my view returns the amp to a purer form.

If it originally had no rear grill or "cord box"... I wonder if the grill and "cord box" were added after a bunch of amps came in for service. It seems to me with a "computer style" electric cord that plugs into the amp vertically, you could do some damage if you grabbed the amp (to move it) and forgot to unplug it first.... the cord box will prevent some of that, and the grill prevents "re-routing" the cord. Just a guess - most computer style electrical cords plug in horizontally instead of vertically.

I'm not saying y'all are crazy or nothing, but this fuss about the front grill seems way out of line. my other Gibson amp's got way more of a screen

http://www.rockhouse.co.kr/shopimages/070600007_c.jpg

and it sounds just fine. Kind of like the GA-5's big brother, actually. Hey, maybe the screen's the secret! I'm going to go rob a confessional and put that screen in front of the speaker on my Bad Cat! I'll report back when I get out of jail.

I'm not saying y'all are crazy or nothing, but this fuss about the front grill seems way out of line. my other Gibson amp's got way more of a screen
http://www.rockhouse.co.kr/shopimages/070600007_c.jpg

and it sounds just fine. Kind of like the GA-5's big brother, actually. Hey, maybe the screen's the secret! I'm going to go rob a confessional and put that screen in front of the speaker on my Bad Cat! I'll report back when I get out of jail.

Good point about that other Gibson grill - and come to think of it, those old Parish priests did seem to hear my sins pretty good through that confessional screen back in the day. :lol:

If it originally had no rear grill or "cord box"... I wonder if the grill and "cord box" were added after a bunch of amps came in for service. It seems to me with a "computer style" electric cord that plugs into the amp vertically, you could do some damage if you grabbed the amp (to move it) and forgot to unplug it first.... the cord box will prevent some of that, and the grill prevents "re-routing" the cord. Just a guess - most computer style electrical cords plug in horizontally instead of vertically.


Like most amps, the power cord on the GA-5 has screw retainer into the cab side for cord stress/strain relief. So the cord box serves some other purpose.

Like most amps, the power cord on the GA-5 has screw retainer into the cab side for cord stress/strain relief. So the cord box serves some other purpose.

I believe it's just to close up the box from small items better.

Look at the internal pics of the new Fender Deluxe reissue. It has a box around the input jacks.

It does all seem a bit much, but such is life in a time when everyone must be protected from themselves.

I just bought a brand new Mesa/Boogie Express 5:50 about a month ago and it has none of these safety items in it!
The tubes and transformers are completely exposed in the back with only an extruded aluminum bar to protect them (not you!).

If you'd like to burn yourself on a hot 6L6, you're free to do so.

Rock and roll is supposed to be dangerous!

Like most amps, the power cord on the GA-5 has screw retainer into the cab side for cord stress/strain relief. So the cord box serves some other purpose.

I think it's just to prevent the plug from going all the way back into the cab so you can't grab it. With the grill in place in back, there's no other access, so you'd have to try to reach in through that little hole and fish around with your finger to try and hook the damn thing out.

Hiya everyone, I've got a GA-5 gig report to share...I had been looking to help bring down our stage volume a bit, so I jumped on this little amp. It's all stock, I don't know a thing about all the wonderful mods you have been chatting about! I did swap out the 12AX7 with a 12AT7 to see if I could get a little more clean headroom...here's my report:

Played a small venue last night, brought this new little gem. Small stage. House held about 100. We are keyboards, bass, drums, and guitar; a Louisiana style zydeco/funk band.

This amp kept up really well, everyone in the band liked it! I put a SM57 on it and sent it through the PA. Up on an amp stand, just next to me, angled across the stage like a monitor. At one point, my bass player stepped back outta line with this thing when I took a solo later in the night (when our volume started to get up there!) It was too loud for her!

This thing is just great for me. Lightweight, packs a great punch. Not a ton of 'at volume' clean headroom, so that was an adjustment. I never once used my Blues Driver, so unnecessary. It was all about twiddling the volume knob on my Strat. I kept the amp around noon or 1 o'clock, never touched it all night. I did use an EQ pedal to give it more high end, and that worked great, I kept it on all night.

Overall, I'm very happy with it and looking forward to gigging it again. In a live situation, there's a learning curve for me when it comes to getting my gain at the guitar, and dialing down for clean. This made it very fun and satisfying to play, a whole new ball game!



droo

I just bought a brand new Mesa/Boogie Express 5:50 about a month ago and it has none of these safety items in it!
The tubes and transformers are completely exposed in the back with only an extruded aluminum bar to protect them (not you!).

If you'd like to burn yourself on a hot 6L6, you're free to do so.

Rock and roll is supposed to be dangerous!

Indeed it is!

Out of curiosity does this amp have the CE symbol on it anywhere?

seems its been discontinued...:(

I'm waiting for Rob's A/B clips. Mine sounds pretty sweet out of the box. No body seems to talk about the room size, furnishings, ambient sound, etc. All real world variables which shape and color sound, possibly negating various "mods".

Hiya everyone, I've got a GA-5 gig report to share...I had been looking to help bring down our stage volume a bit, so I jumped on this little amp. It's all stock, I don't know a thing about all the wonderful mods you have been chatting about! I did swap out the 12AX7 with a 12AT7 to see if I could get a little more clean headroom...here's my report:

Played a small venue last night, brought this new little gem. Small stage. House held about 100. We are keyboards, bass, drums, and guitar; a Louisiana style zydeco/funk band.

This amp kept up really well, everyone in the band liked it! I put a SM57 on it and sent it through the PA. Up on an amp stand, just next to me, angled across the stage like a monitor. At one point, my bass player stepped back outta line with this thing when I took a solo later in the night (when our volume started to get up there!) It was too loud for her!

This thing is just great for me. Lightweight, packs a great punch. Not a ton of 'at volume' clean headroom, so that was an adjustment. I never once used my Blues Driver, so unnecessary. It was all about twiddling the volume knob on my Strat. I kept the amp around noon or 1 o'clock, never touched it all night. I did use an EQ pedal to give it more high end, and that worked great, I kept it on all night.

Overall, I'm very happy with it and looking forward to gigging it again. In a live situation, there's a learning curve for me when it comes to getting my gain at the guitar, and dialing down for clean. This made it very fun and satisfying to play, a whole new ball game!



droo

That's excellent if using the 12AT7 takes care of it for you.

I'm not trying to push anyone to do any mods that they don't want to, or feel comfortable with. I just want to explain that when you sub lower gain tube like a 12AT7, it lowers the gain of the first stage, which is exactly what needs to be done to get a "clearer" tone with more headroom. Problem is, it also lowers the gain, or "cripples" the second stage, which was fine already with a 12AX7.

Simply lifting the lead on the 25uF bypass cap on the first stage, removes it from the circuit, which reduces its gain to an appropriate level with a 12AX7, so that the second stage is not effected.

http://www.specialtyguitars.com/images/ebay/caplift.jpg

Again, I'm not suggesting anyone do anything they are not comfortable with, but if you can solder a pickup in your guitar, you can do this. And easily solder it back if you don't like the mod.

seems its been discontinued...:(

Amazon.com still shows them for $299

Lemme tell ya folks, the mods suggested by specialty - removing the vol pot's inline 1m/22pf and the 1st stage 25uf, adding a 47k NFB - will simply take this amp to a new level of sonic values that you, like me, may find really wakes up an already great little amp. IMO, these are required mods to make this amp circuit become the best it can be - for now.

Indeed it is!

Out of curiosity does this amp have the CE symbol on it anywhere?

Nope. No CE, no UL. Nothing.

Nope. No CE, no UL. Nothing.

That figures.

Like I said, I'm pretty certain it's the European (CE) safety regs that require it so that there is no way at all that a man, woman, child, or pet can possibly touch a hot tube in a guitar amp.


My GA5 and the manual both have the CE logo on them...

Sweetwater now has them for $399 LOL

http://www.sweetwater.com/store/detail/GA5/

OOPS: I see now they're on order, not in stock.

Interesting.

Lemme tell ya folks, the mods suggested by specialty - removing the vol pot's inline 1m/22pf and the 1st stage 25uf, adding a 47k NFB - will simply take this amp to a new level of sonic values that you, like me, may find really wakes up an already great little amp. IMO, these are required mods to make this amp circuit become the best it can be - for now.

Excellent Rob. Glad to help.

Did you find the 47K NFB made it sound more late 50's sounding, like a 5F1?

Excellent Rob. Glad to help.

Did you find the 47K NFB made it sound more late 50's sounding, like a 5F1?

YES! The amp now has more depth and fullness, a smoother overdrive that kicks in a bit later, no change to the generous volume and more "lushness" to the tone. Much closer in tone now to a Li'l Dawg Champster Special.

Any more thoughts on the ground buss?

I just ordered out a Weber 8F150, which should elevate this amp to the Nirvana level (and I don't mean the band)!

When I get #1 it all together I'll begin the A/B tests with the stock #2 - in about 10 days (Weber needs that time to build the speaker).

Simply lifting the lead on the 25uF bypass cap on the first stage, removes it from the circuit, which reduces its gain to an appropriate level with a 12AX7, so that the second stage is not effected.

http://www.specialtyguitars.com/images/ebay/caplift.jpg



Specialty guitars...I do want to try this mod! Thanks for the excellent pictures and clear advice :)

One question, a totally basic newbie thing...do I simply cut that lead as close as I can? Is that what you call "lifting"?

Androo-

Stay away from the positive leads of those larger blue caps or anything that they're connected to when you're in there! They can hold a large charge even when the amp is unplugged and can hurt you badly!

Be carefull, even when taking the ampo apart, that your fingers don't slip in there and touch any electronic parts that they're not supposed to.

These amps are not toys!

Specialty guitars...I do want to try this mod! Thanks for the excellent pictures and clear advice :)

One question, a totally basic newbie thing...do I simply cut that lead as close as I can? Is that what you call "lifting"?

No problem. By "lifting" this capacitor, in this case, we mean unsoldering one of the leads.

The lead from the black capacitor in the photo, the lead with the arrow drawn in pointing at it, bends to the right, and is soldered to the post along with that resistor and white wire. You simply unsolder that cap's lead from that post, as shown in the photo. (I didn't bend it away very far from the post, so it is not obvious) This removes the capacitor from the circuit. You can see what you think, and if you don't like the change, you can solder it back to the post. But I'm certain you will like the results.

Androo-

Stay away from the positive leads of those larger blue caps or anything that they're connected to when you're in there! They can hold a large charge even when the amp is unplugged and can hurt you badly!

Be carefull, even when taking the ampo apart, that your fingers don't slip in there and touch any electronic parts that they're not supposed to.

These amps are not toys!

Very good points Red!

Yes, unplug the amp.

Discharge the filter caps if you know how, otherwise steer clear of them as Red said.

Like most amps, the power cord on the GA-5 has screw retainer into the cab side for cord stress/strain relief. So the cord box serves some other purpose.

My cord was completely inside the box when I unwrapped it but I cant see anyone actually going to all that trouble to coil it up and put it back. The 10' I replaced it with wouldnt fit anyway!:lol:

.
.
.

:shock: !!!! WE ALL NEED TO BE AWARE OF THE IMMINENT LETHALITY OF TUBE AMPS !!!! :shock:

It helps to at least drain the filter caps before sticking human digits into the chassis!!!

Quick 'n' dirty filter cap drain - plug in the amp, plug in a guitar, while strumming the guitar reach over and pull out power cord - keep strumming - you'll hear the sound gradually fade off to silence ... the caps are now reasonably drained and won't kill you too much. :cool:

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.
.

:shock: !!!! WE ALL NEED TO BE AWARE OF THE IMMINENT LETHALITY OF TUBE AMPS !!!! :shock:

It helps to at least drain the filter caps before sticking human digits into the chassis!!!

Quick 'n' dirty filter cap drain - plug in the amp, plug in a guitar, while strumming the guitar reach over and pull out power cord - keep strumming - you'll hear the sound gradually fade off to silence ... the caps are now reasonably drained and won't kill you too much. :cool:

Yeah, I know I was guilty of getting caught up in the fun, being completely remiss in mentioning the safety stuff.

Are we missing any members who posted earlier on this thread? :oops:

I don't want to derail a good tech discussion...but I got pulled into buying one of the GA-5s from MF through this thread....what an awesome little amp. I absolutely love it. Knowing that I'll never get huge bass response from a 5w amp in a tiny cab, is there anything I can do to maximize/tighten the bass a bit?

Got it. Thank you so much for reminding me, and everyone. I don't know much about the innards at all, but I do know they can be very, very dangerous.

I will do as you said Rob, a quick and dirty drain. Is there any other things I should do to stay safe?

#1 quick and dirty drain (don't throw the power switch to turn it off, but pull the cord out of the wall while playing and keep playing, yes?)
#2 be careful not to touch much when I take out the chassis
#3 don't touch the blue cap or anything that looks like it's connected to it.
#4 unsolder that lead from the post, bend it out of the way a bit.

Anything else?

droo

I don't want to derail a good tech discussion...but I got pulled into buying one of the GA-5s from MF through this thread....what an awesome little amp. I absolutely love it. Knowing that I'll never get huge bass response from a 5w amp in a tiny cab, is there anything I can do to maximize/tighten the bass a bit?

Go back in this thread to page 6, or further back, and read forward.

I don't want to derail a good tech discussion...but I got pulled into buying one of the GA-5s from MF through this thread....what an awesome little amp. I absolutely love it. Knowing that I'll never get huge bass response from a 5w amp in a tiny cab, is there anything I can do to maximize/tighten the bass a bit?


Perform all three mods that specialty guitars has outlined - these tweaks will really open up the GA-5.

For maximum bass response, install a beefier ceramic speaker such as a Weber 8F150, or AlNiCo such as the Weber 8A150.

Got it. Thank you so much for reminding me, and everyone. I don't know much about the innards at all, but I do know they can be very, very dangerous.

I will do as you said Rob, a quick and dirty drain. Is there any other things I should do to stay safe?

#1 quick and dirty drain (don't throw the power switch to turn it off, but pull the cord out of the wall while playing and keep playing, yes?)

YES.

#2 be careful not to touch much when I take out the chassis
#3 don't touch the blue cap or anything that looks like it's connected to it.
#4 unsolder that lead from the post, bend it out of the way a bit.

I didn't even bother unsoldering the cap - just clipped one side off ... the green arrows show the red jumper wire added and the clipped cap lead ...

http://img.photobucket.com/albums/v82/rfdee/circuitmods.jpg

Anything else?

ADD THE 47K NFB RESISTOR - YOU'LL LOVE IT!

http://www.specialtyguitars.com/images/ebay/nfb.jpg

droo

....

where can i get that last resistor Radio Shack?

where can i get that last resistor Radio Shack?

Sure. A 47k 1/2 watt of any type will be fine.

i tried putting a new tung sol ri 12ax7 and it wont fit! thats my most favorite pre tube and it wont fit! i tried two of em. anyone have luck with that tube?

where can i get that last resistor Radio Shack?

Yep, 99 cents for five of 'em (47K).

Another "mod" I just made was to add a tube shield for the 12AX7 - believe this does help with noise, dunno why Gibson didn't supply one in the first place, prolly cost them 10 cents.

Recap of my GA-5 mods to date ...

CIRCUIT (as of 3/7)
* 1m resistor and 22pf cap removed and jumpered
* 1st stage 25uf cap lifted
* 47k NFB added
* 1/4" external 8 ohm speaker jack added
* add tube shield to the 12AX7 preamp tube
* add HD alum foil to inside cab top and sides, down into the cab's chassis slots
* replace the 2-way power switch with a Carling 3-way for off/standby/on - this will help with tube life since the rectifier is solid state - this mod is in progress ...

SPEAKER
* Weber 8F150 - awaiting arrival next week (I hope)

CAB
* remove the power cord box
* remove the rear grille
* rebaffle with 1/2" birch ply and cane grille - awaiting the speaker

Any more thoughts on the ground buss?

The 47K NFB resistor did more to lower the 60hz hum, than any hum reducing trick I could remember. So if you like that mod, it will help the hum that these types of amps are prone to.

I tried all sorts of things to reduce noise and hum, with limited success. I isolated the preamp grounds from the power amp grounds. Didn't seem to make a difference. I moved the 100 ohm resistors that make and artificial ground tap for the heater wires, from the preamp area of the board, to the pilot light, tried grounding it at the power amp ground buss, and to the top of cathode bypass resistor for the power tube (this is an old trick that works sometimes). Not sure if any of this went any more forwards than backwards.

The thing that made the most difference in noise was shielding the top and edges of the cabinet with heavy duty aluminum foil. Amps spray a lot of noise, that tends to wreak havoc with single coils. Shielding the cab completely seals the electronics electrically, which reduces that crap quit a bit.

I'll post some pics later.

The 47K NFB resistor did more to lower the 60hz hum, than any hum reducing trick I could remember. So if you like that mod, it will help the hum that these types of amps are prone to.

Yep, the noise suppression was immediately noticed when the NFB was added.

I tried all sorts of thins to reduce noise and hum, with limited success. I isolated the preamp grounds from the power amp grounds. Didn't seem to make a difference. I moved the 100 ohm resistors that make and artificial ground tap for the heater wires, from the preamp area of the board, to the pilot light, tried grounding it at the power amp ground buss, and to the top of cathode bypass resistor for the power tube (this is an old trick that works sometimes). Not sure if any of this went any more forwards than backwards.

The thing that made the most difference in noise was shielding the top and edges of the cabinet with heavy duty aluminum foil. Amps spray a lot of noise, that tends to wreak havoc with single coils. Shielding the cab completely seals the electronics electrically, which reduces that crap quit a bit.

I do exactly that to all my amps and was thinking about that yesterday, then forgot about it. I use Reynolds heavy duty aluminum foil, spray on some 3M spray adhesive cement, fit to the cab top - in the case of the GA-5, the foil should run down the sides and into the chassis slot to complete the ground. Alum foil makes for a good noise shield.

I'll post some pics later.

....

I'm afraid it's not pretty. Did this LATE last night. I opted to leave the tracks clear, and bring some foil around the edges where the chassis screws on to ground the shielding.

http://www.specialtyguitars.com/images/ebay/shield.jpg

http://www.specialtyguitars.com/images/ebay/shield2.jpg

Recap of my GA-5 mods to date ...

CIRCUIT (as of 3/7)
* 1m resistor and 22pf cap removed and jumpered
* 1st stage 25uf cap lifted
* 47k NFB added
* 1/4" external 8 ohm speaker jack added
* add tube shield to the 12AX7 preamp tube
* add HD alum foil to inside cab top and sides, down into the cab's chassis slots
* replace the 2-way power switch with a Carling 3-way for off/standby/on - this will help with tube life since the rectifier is solid state - this mod is in progress ...

SPEAKER
* Weber 8F150 - awaiting arrival next week (I hope)

CAB
* remove the power cord box
* remove the rear grille
* rebaffle with 1/2" birch ply and cane grille - awaiting the speaker

Rob, what did you think of the 22pF across the volume control?

Rob, what did you think of the 22pF across the volume control?

First, good job on the foil shield - it can be a pain to do.

I didn't particularly like the 22pf bleeder cap (across the input and wiper lugs) - I like the smoother, darker response of the amp's tone as its vol pot was cranked. IOW, I feel the tone gets fatter and meatier as the amp vol is increased. Now I get a great, greasy blues tone at 2pm on dial (using a Strat loaded with Keystones or a Tele with Rio Tallboys) ... to my ears, this tone is just perfect. At slightly lower volumes 11 to noon, it cleans up enough for crisp fingerstyle ragtime or blues pickin' Wouldn't have happened without yer 3 killer mods - thanx again!

I think I'll work on some A/B mp3 demos 'tween the two amps before #1 gets the speaker mod.

This is my first post on this forum even though I have lured for years. This amp loves P-90's, Open G, and slide. I am liking it a lot so far. I am going to give it a few weeks until the honeymoon is over before I review it. It has been a while since I have used the guitar controls this much, but that is one of the keys to this amps tone.

This is my first post on this forum even though I have lured for years. This amp loves P-90's, Open G, and slide. I am liking it a lot so far. I am going to give it a few weeks until the honeymoon is over before I review it. It has been a while since I have used the guitar controls this much, but that is one of the keys to this amps tone.

Yes, I totally agree - in stock format the the GA-5 begs to be controlled by yer guitar's vol and tone pots. However, after the 3 main circuit mods the amp behaves a lot tamer and works even better to allow yer guitar's tone to shine through. IMO.

First, good job on the foil shield - it can be a pain to do.

I didn't particularly like the 22pf bleeder cap (across the input and wiper lugs) - I like the smoother, darker response of the amp's tone as its vol pot was cranked. IOW, I feel the tone gets fatter and meatier as the amp vol is increased. Now I get a great, greasy blues tone at 2pm on dial (using a Strat loaded with Keystones or a Tele with Rio Tallboys) ... to my ears, this tone is just perfect. At slightly lower volumes 11 to noon, it cleans up enough for crisp fingerstyle ragtime or blues pickin' Wouldn't have happened without yer 3 killer mods - thanx again!

I think I'll work on some A/B mp3 demos 'tween the two amps before #1 gets the speaker mod.

Thanks.

Right on.

Yeah, I'm 50/50 on the treble bleed cap. My amp is dark when down low, which is what that mod helps. As you turn up the volume knob, the cap has less and less effect. The amp brightens naturally from the resistance being decreased (same as on a guitar), at the same time, the cap is having less and less effect on the circuit because the resistance on its side of the pot is increasing as the volume is turned up. In theory, with the right pot value, cap value etc. the tone should stay even. But as with guitar volume controls, there are all sorts of treble bleed arrangements, and to my ears, it never quite works perfectly with any of them.

Those A/B demos would be a kick!

I have been following this thread with some interest
I missed out on getting one of these from MF
wondering if anyone has tried lowering the cathode resistor on v1
down to 1k5 or 820 ohms
I would think that would give you a little more voltage and make the distortion not so fizzy
I believe the stock resistor is 2k2 or 2k7 ??

Dan..........

These are highly tunable little amps. You could use the mods that are well documented in the FAQ section of the VJ part of SEWATT.com. There are some very simple mods, i.e. changing one or two resistor values and cap values to fine tune the amp into a Marshall, Vox, Fender or many more exotic sounding amps. See attached file for some basic mods.

Dan,

Gee posted a link that describes that and more that can be done to "tune" the circuit.

But losing the cathode bypass cap on the first 2.2K does wonders to clean the amp up. But, nothing wrong with going to 1.5K or any of the other possible mods.

I just removed the metal grills and cord box, jumpered the 22pF cap/1m resistor, disconnected the 25uF bias bypass cap and added a 47k NFB on my GA5.

The amp sounds awesome! I was hesitant to modify the amp because I wasn't sure that I was going to keep it. I liked it, but wasn't completely impressed with the tone, My 5E3 clone was killing it and wasn't so much louder that the GA5 would be useful to me.

For me, removing the rear metal grill and cord box was mandatory. They were easy to remove and it makes the amp easier to move, store, swap tubes on and connect speakers to.

Removing the front grill was a pain in the butt! Don't bother unless you have a condition where you can't leave well enough alone!!! It came out fine and I really do believe that it improved the tone, but not nearly as much as the electronic mods.

I'm very impressed with the electronic mods. I did them one at a time starting with jumpering the 22pF cap/1m resistor, disconnecting the 23uF byass bypass cap and adding the NFB.

I like the first two mods more than the NFB. I'm not sure of that one yet.

The amp is vastly better with a Telecaster now. In fact, it's a match made in heaven.
It's a mix of Champ tones and Vox chime. I still prefer the amp for clean to semi dirty tones. My 5E3 still kills it on songs like Funk #49 though!
The amp is chimey and rich where it was boxy before. It's much more responsive to the guitar's volume control. As much as my 5E3 clone.

The NFB seems to make the amp a tad too middy with my Les Paul and PRS Soapy.

Cranked way up the amp is still too out of control for my liking. That might be the EL-84. That's fine the clean and semi dirty tones more than make up for it. Maybe it could be even better tuned with a few more mods, a 820 to 1K5 cathode bias resistor on V1 as dansamp suggested, for instance.

I'm impressed!

Now the sons of guns at MF offer me a 10 percent off coupon, now that the blessed things are gone.
Ah, it ain't no fun unless it is a game; I couldn't just pay the three bills and be done with it.

I'm thinking of tweaking/testing the NFB further - a 100k or 200k trimpot on one side of a DPDT switch. The trimpot would allow finding the NFB resistance sweet spot and the switch would allow removing the NFB completely.

I'm thinking of tweaking/testing the NFB further - a 100k or 200k trimpot on one side of a DPDT switch. The trimpot would allow finding the NFB resistance sweet spot and the switch would allow removing the NFB completely.

I noticed that as the value of the resistor increased, so did that 60 hz hum that it helped tame, but on the good side, it brings back more of the gainy rawness and brightness. So it wouldn't hurt to experiment.

Like I said before, a 250K no-load pot would get you about all the variance you need. You could wire it in series with a 10K resistor, and be able to go from 10K to 260K to open (non NFB). Just for an example.

One thing you could try Red, is to try the 47k NFB resistor, but remove the jumper from the 22pf/1 meg filter. that arrangement may work better with humbuckers.

Dan,

Gee posted a link that describes that and more that can be done to "tune" the circuit.

But losing the cathode bypass cap on the first 2.2K does wonders to clean the amp up. But, nothing wrong with going to 1.5K or any of the other possible mods.
Yes. You really will save yourselves a lot of time and experimental effort if you read the Valve Junior FAQ (http://www.sewatt.com/vj-faq) on the SEWATT site

The Valve Junior circuit is effectively the same as the GA-5 and that circuit has gone through an evolution with the VJ modding community that has probably never happened with any other amp. Several thousand people with some of the best brains and ears in the amplifier community working constantly for the last 2 years. That is a serious amount of R&D!

Some of the key things to check and alter are:
1. The EL84 will sound at its best with about 310V or less on it. Usually the PT's used in these amps are Champ 6V6 PT's that produce way too much voltage making the EL84 sound harsh. A VVR circuit or a string of high power zeners will fix the problem.
2. EL84's can sound harsh when pushed and to some people they produce too much treble as the gain increases. This can be cured by replacing the 25uF EL84 cathode cap with a 1000uF cap and/or adding a conjunctive filter just like the Carmen Ghia or Hammond AO-35.
3. The breakup and gain of the amp is set by the voltage divider resistors and the first preamp cathode cap value. You can change these to taste and enjoy. This is where you tune the amp to your gain, breakup point, character and playing style.
4. Making the negative feedback switchable with a center off DPDT switch and 2 different resistor values is also a good mod.

The real beauty of the GA-5 is that you can pull the chassis out quickly and change the components in a couple of minutes because of its turret board construction.

Working on valve amps can seriously damage your health and life - the initial shock from the charged capacitors may not kill you, but flying backwards across the room may do. All of these mods should only be undertaken when you have familiarized yourself with the dangers and taken the correct precautions. Otherwise get someone qualified to do this stuff for you.

The external 8 ohm speaker jack can automatically turn off the internal speaker.

It takes a special 1/4" Switchcraft jack, part number 13E (tubesandmore is one vendor that has 'em for a $1.50, part S-H535). When the external jack isn't used, the interal jack switch is closed to allow the 4 ohm load to the internal RCA jack. When ya plug in the 1/4" jack to turn on an external speaker cab, the jack's switch is opened and automatically disconnects the internal speaker ....

http://img.photobucket.com/albums/v82/rfdee/ext-jack.jpg

I'm looking for an amp and Musician's Friend is sold out. I live in Ontario, anyone know where to get one of these?????

Yes. You really will save yourselves a lot of time and experimental effort if you read the Valve Junior FAQ (http://www.sewatt.com/vj-faq) on the SEWATT site


This is a site worth joining!

1. The EL84 will sound at its best with about 310V or less on it. Usually the PT's used in these amps are Champ 6V6 PT's that produce way too much voltage making the EL84 sound harsh.

I would assume that the mojo transformers in the Gibson are different than the Epi transformers. I looked at the mojotone site to see if they have any specs on the mojo778 transformer. I could not find any voltage info.

Has anyone recorded the different voltages from the power supply? And around the tubes?

SAFETY QUESTION!

Hey folks, I'm thinking of trying the two mods today, the jumper and the lifted bypass cap. My question is in regard to draining.

I've been reading information that the quick and dirty draining method of "blind switching" only works on amps with a standby switch.

What are your thoughts?

Thanks so much everyone!
droo

SAFETY QUESTION!

Hey folks, I'm thinking of trying the two mods today, the jumper and the lifted bypass cap. My question is in regard to draining.

I've been reading information that the quick and dirty draining method of "blind switching" only works on amps with a standby switch.

What are your thoughts?

Thanks so much everyone!
droo

I don't think the "quick & dirty" way is ever an option. I ALWAYS drain the filter caps and I keep a resistor clipped in as long as I'm working on it.

I don't want to get bit.

I drain the filter caps to ground through a resistor every time I open an amp. It's the only safe thing to do.

I made a device using a test lead and a resistor several years ago. I don't remember the value and wattage of the resistor. Maybe 100k, 10 watts?
I actually leave it connected the whole time that I work on the amp.

1. The EL84 will sound at its best with about 310V or less on it. Usually the PT's used in these amps are Champ 6V6 PT's that produce way too much voltage making the EL84 sound harsh. A VVR circuit or a string of high power zeners will fix the problem.


I just read the voltages on my power supply.

A = 308VDC
B = 264VDC
C = 242VDC

These are stock. I have not modded anything.

I hope this helps others out. And thanks Gee for the great information. I did not know about that other forum you pointed out. The items you listed are a great place to start looking.

SAFETY QUESTION!

Hey folks, I'm thinking of trying the two mods today, the jumper and the lifted bypass cap. My question is in regard to draining.

I've been reading information that the quick and dirty draining method of "blind switching" only works on amps with a standby switch.

What are your thoughts?

Thanks so much everyone!
droo


Running the amp and pulling the power cord while strumming the plugged in guitar will drain the filter caps down to SOME level.

The best way to drain the filter caps is with a probe/resistor to ground. And even then, use a VOM to check for voltage.

I just read the voltages on my power supply.

A = 308VDC
B = 264VDC
C = 242VDC

These are stock. I have not modded anything.

I hope this helps others out. And thanks Gee for the great information. I did not know about that other forum you pointed out. The items you listed are a great place to start looking.
Perfect! Looks like Gibson have done everything right with the GA-5.

I am just struggling with this.

The tweaker in me wants to mess with this amp. But, I really think it sounds great how it is.

Not every guitar sounds great in every amp. This amp is no exception. Not all of my guitars sound great in it. Some guitars just match up better with certain amps.

But my ASAT Classic (tele - for the most part) works great with this amp. I still might end up with a lower gain preamp tube. But right now, if I just put the amp at 1/2 to 3/4 up, I can get a fantastic clean to overdriven sound with a twist of the volume on my guitar. I think the ASAT Classic works so well because it does have a treble bypass cap on the volume knob (stock) so it doesn't get muddy when turned down. Some of my other guitars mud up with this amp when I roll back the volume.

The secret is finding what combination of gear works, and using it.

Running the amp and pulling the power cord while strumming the plugged in guitar will drain the filter caps down to SOME level.

The best way to drain the filter caps is with a probe/resistor to ground. And even then, use a VOM to check for voltage.


Could you check my thoughts on this? I'm going to head out and get a meter before I try anything. I've read 2 ways:

A. connecting (insulated) alligator-jumper-alligator, then from chassis to pin #1 of preamp tube socket....looking at the pictures of the above mods, which pin would be pin #1?

B. solder two leads to a 2 watt/27k resistor and put some alligator clips on the ends. Clip one end of the drainer to the chassis and then, clip the other to each filter cap until it's drained. Which end of cap is the correct end for this procedure?

Do my questions make you feel as if I should not attempt this? :?:
droo

I'm still trying to get sounds I like out of this amp. But, I did try my Dano U-2 and it sounds really good. Great Rock n Roll sound. It's the best for me so far. I'm hoping that the speaker will eventually break in and make me smile.

Could you check my thoughts on this? I'm going to head out and get a meter before I try anything. I've read 2 ways:

A. connecting (insulated) alligator-jumper-alligator, then from chassis to pin #1 of preamp tube socket....looking at the pictures of the above mods, which pin would be pin #1?

B. solder two leads to a 2 watt/27k resistor and put some alligator clips on the ends. Clip one end of the drainer to the chassis and then, clip the other to each filter cap until it's drained. Which end of cap is the correct end for this procedure?

Do my questions make you feel as if I should not attempt this? :?:
droo

Either is fine. Method A is the easiest to assemble. It drains the caps slowly through all of the series resistors in the power supply.

Hi guys. I have been following this thread with great interest! I ordered one of these amps last week. Being in Ontario, it may take another week or so to arrive. I'm just revvin' to get my hands on it! I'm very thankful to all of you with the knowledge and ability to figure out the tweaks to take a great amp and make it brilliant. If you don't mind, I will mooch the ideas that I think will suit me. Keep up the good work!

On a side note: There was this kid waaay back when in electronics class fiddling around with a non-descript camera flash. He landed up on his @55 ten feet from where he was sitting after poking at an innocent looking cap. For those new at fiddling and testing gear, take all precautions.

If I might post a link to a web page I came across, it has extremely good info on knocking down the charge in caps safely: http://studentweb.eku.edu/justin_holton/caps.html

Thanks again and keep the ideas flowing!

G Man

B. solder two leads to a 2 watt/27k resistor and put some alligator clips on the ends. Clip one end of the drainer to the chassis and then, clip the other to each filter cap until it's drained. Which end of cap is the correct end for this procedure?


This is what I do, though I think my resistor is bigger.

Make sure that the alligator clips are well insulated. You'd hate to get electrocuted while trying to protect yourself from being electrocuted!

One side of the cap connects to ground, the other end connects to the circuit. Drain the end that's connected to the circuit. I leave the clips attached until I'm done working on the amp. Remember to remove them before you turn the amp back on.

Check for voltage with a meter.

Anybody still looking for one:

There's one for sale at 299 + shipping from Fishkill, NY, on the FDP

http://www.fenderforum.com/classified.html?ad=23877

In the past I always drained caps using a simple analog voltage meter. Digital versions don't seem to work. Place it on a high ac setting and touch the probes to both sides of a capacitor. You can watch the needle dropping as the caps are being drained. Takes about 3-5 seconds.

The resistors within are doing the same draining function as the resistor-to-ground method mentioned earlier, and you also have visual proof the act is occurring. Of course, double-checking with a digital meter is always advised.

http://www.weisd.com/store2/BK%20117B.jpg

If someone could monitor the voltage when the power is turned off then you may find that the caps drain naturally. Otherwise you could put a resistor of about 220K (1W) across the first power cap and then the amp will drain within 20 secs or so after the amp is turned off.

It is always good life prolonging practice to check the caps voltage every time you work on it anyway.

If someone could monitor the voltage when the power is turned off then you may find that the caps drain naturally.

You may but not always.

The first time I ever watched an amp being serviced, the tech drained the caps but shorting them to ground with a screwdriver. It made a loud crack noise and sparks.

The amp hadn't even been plugged in since the night before.

Electrolytic caps can and often will carry lethal voltages in them even after the amp is unplugged for a long time!

Even after you've drained the caps, the voltage can come back up, even with the amp unplugged. If you leave a digital volt meter connected you can actually see this happening.

Drain the caps every time your in there!!! It's the only way to be safe!!!

You may but not always.

The first time I ever watched an amp being serviced, the tech drained the caps but shorting them to ground with a screwdriver. It made a loud crack noise and sparks.

The amp hadn't even been plugged in since the night before.

Electrolytic caps can and often will carry lethal voltages in them even after the amp is unplugged for a long time!

Even after you've drained the caps, the voltage can come back up, even with the amp unplugged. If you leave a digital volt meter connected you can actually see this happening.

Drain the caps every time your in there!!! It's the only way to be safe!!!

+1 http://img.photobucket.com/albums/v82/rfdee/thumbsup.gif http://img.photobucket.com/albums/v82/rfdee/thumbsup.gif

Here you go Rob. For the GA5 modder who has everything, how about a power cord strain relief that fits the cord properly?

http://www.specialtyguitars.com/images/ebay/clip.jpg

http://www.specialtyguitars.com/images/ebay/clip2.jpg

I bought a couple of these from Dynakit a year or so ago, and stumbled across them yesterday.

I've got one of your 3 pos DPDT switches on the way to add a Standby, and I think after that, and some spiffy new grill cloth, I'll call it good...

Here you go Rob. For the GA5 modder who has everything, how about a power cord strain relief that fits the cord properly?

http://www.specialtyguitars.com/images/ebay/clip.jpg

http://www.specialtyguitars.com/images/ebay/clip2.jpg

I bought a couple of these from Dynakit a year or so ago, and stumbled across them yesterday.

I've got one of your 3 pos DPDT switches on the way to add a Standby, and I think after that, and some spiffy new grill cloth, I'll call it good...

Hmm, both my GA-5's came with a very nice power corder retainer ...

http://img.photobucket.com/albums/v82/rfdee/strain.jpg

I use Carling Progressive Circuit DPTTP switches exclusively ...

http://westlabs.com/Switches.jpg

"Carling Double Pole Triple Throw PROGRESSIVE (switch image on far right)

This is a two circuit, three position switch.
In the bottom position, both circuits are off.
In the middle position. one circuit is on.
In the top position, both circuits are on.

THIS IS THE SWITCH THAT ALLOWS YOU TO
HAVE BOTH A POWER ON-OFF, AND A STANDBY
SWITCH, IN THE SAME HOLE !!!"

That's a great switch.

If you don't mind, please post details on the install and where to get the switch.

I'm also looking forward to hearing how an alnico speaker sounds in these amps.

That's a great switch.

Nope, yer wrong - it's an AMAZING switch !!!!!! :mrgreen:

If you don't mind, please post details on the install and where to get the switch.

Get it here - www.westlabs.com - $9 each.

I'm also looking forward to hearing how an alnico speaker sounds in these amps.

AlNiCo's rarely are my cup of tea these dayze, particularly the smaller 8" variety. It takes a really robust AlNiCo RING mag speaker (not a plug mag) to make any kinda good difference, and those kinda speakers are tres expensive.



....

Hmm, both my GA-5's came with a very nice power corder retainer ...


Mine came with a white one as well, but it didn't actually pinch the cord to hold it firmly. It was too large for the diameter of the cord, and the cord was loose inside it. No big deal, but the idea is for the clip to hold the cord firmly, and I happened to have these on hand...

What is the advantage of the triple switch?

To prolong tube life?

(I am much enjoying my GA-5 unmodded except for removal of the metal grates and cord box.)

Mine came with a white one as well, but it didn't actually pinch the cord to hold it firmly. It was too large for the diameter of the cord, and the cord was loose inside it. No big deal, but the idea is for the clip to hold the cord firmly, and I happened to have these on hand...

The white ones grip the power wire pretty tight. I used make up retainers outta wide cable ties. :cool:

What is the advantage of the triple switch?

To prolong tube life?

(I am much enjoying my GA-5 unmodded except for removal of the metal grates and cord box.)

It can really help to have a standby with a s/s rectified amp because that recto circuit will whack a full load to the tubies whereas a recto tube will soften the blow. The Carling switch gives you the three functions of separate on/off and standby switches, all in one switch = one less hole to drill in the control panel. Besides, it just works better/easier = down is off, middle is standby, top is on. :cool:

.... (I am much enjoying my GA-5 unmodded except for removal of the metal grates and cord box.)

Dude, you've really gotta try the specialty guitars circuit mod trio.

Dude, you've really gotta try the specialty guitars circuit mod trio.

:lol:

They all looked very doable with my tools and ok skill level and experience poking around in amps -but I think I understood the point of them to be more headroom? Me, I like breakup . . . . will have to re-read posts . . . .

(As an aside I compared the GA-5 to my stock '68 Champ with both dimed through my Telecaster - the GA-5 is noticeably louder. As others have noted a LOUD 5 watts.)

The white ones grip the power wire pretty tight. I used make up retainers outta wide cable ties. :cool:

I think mine came with a smaller diameter cord than yours. I replace my cord, but it's the same diameter as the original.

But really, like I said, it's for the "modder with everything" as I wouldn't have paid it any mind had I not stumbled across the smaller clips that I didn't know I already had.

AlNiCo's rarely are my cup of tea these dayze, particularly the smaller 8" variety. It takes a really robust AlNiCo RING mag speaker (not a plug mag) to make any kinda good difference, and those kinda speakers are tres expensive.

I've got a Weber 12A125 in my 5E3 clone that I love. I've tried others in there and they just wouldn't do. I was hoping for the same kind of thing with a Weber 8A100.
Of course, I wouldn't expect the same tone from an 8 incher, though!

I think mine came with a smaller diameter cord than yours. I replace my cord, but it's the same diameter as the original.

But really, like I said, it's for the "modder with everything" as I wouldn't have paid it any mind had I not stumbled across the smaller clips that I didn't know I already had.

The modding bug bites hard and deep. :twisted:

:lol:

They all looked very doable with my tools and ok skill level and experience poking around in amps -but I think I understood the point of them to be more headroom? Me, I like breakup . . . . will have to re-read posts . . . .

(As an aside I compared the GA-5 to my stock '68 Champ with both dimed through my Telecaster - the GA-5 is noticeably louder. As others have noted a LOUD 5 watts.)

Just do the mods.

It's near impossible to describe the subtleties of sonics with mere words. The mods are not at all gonna make ya lose that treble bite or volume level - it's about fattening up and smoothing out the tone and overdrive, and the NFB will quiet things down lots more.

Just do the mods.

Just do the mods.

It's near impossible to describe the subtleties of sonics with mere words. The mods are not at all gonna make ya lose that treble bite or volume level - it's about fattening up and smoothing out the tone and overdrive, and the NFB will quiet things down lots more.

Just do the mods.


Aye, aye, Cap'n!

So you guys say that little resister is available at my neighborhood Radio Shack?

Will report back later this week.

Aye, aye, Cap'n!

So you guys say that little resister is available at my neighborhood Radio Shack?

Will report back later this week.

Yep - 47K resistor, 1/2 watt, 5% tolerance - 99 cents for 5 of 'em.

I don't want to derail a good tech discussion...but I got pulled into buying one of the GA-5s from MF through this thread....what an awesome little amp. I absolutely love it. Knowing that I'll never get huge bass response from a 5w amp in a tiny cab, is there anything I can do to maximize/tighten the bass a bit?

Not having this particular amp myself, but looking at the schematic, you might try a lower value resistor in the power supply to the screen grids, something like 1K instead of the 10K (between the A and B points), that should give it more punch.

Aye, aye, Cap'n!

So you guys say that little resister is available at my neighborhood Radio Shack?

Will report back later this week.

From Radio Shack's website-

47K ohm 1/2W 5% Carbon Film Resistor pk/5
Model: 271-1130 | Catalog #: 271-1130
$0.99

If you have any problems getting them e-mail me your mailing address and I'll put one in the mail to you.

Yes got some yesterday, Thanks Rob. Now where do I get the switch, did not think to look for one when I was in there but its just down the road.

Yes got some yesterday, Thanks Rob. Now where do I get the switch, did not think to look for one when I was in there but its just down the road.

Read post #370 on this thread.

+1 http://img.photobucket.com/albums/v82/rfdee/thumbsup.gif http://img.photobucket.com/albums/v82/rfdee/thumbsup.gif

Rob you are my go to guy for amps!!!... :cool:

Rob you are my go to guy for amps!!!... :cool:

Hah! You really think I know what I'm doing???!!! :shock:

Rob, another mod you might want to try, that I forgot to mention...

This is no huge deal, but I'm surprised that Gibson did this, as they are isolating the input jacks from the chassis. Notice how they grounded the one leg of the volume pot, to its housing using the lead of the resistor? I'm surprised they did this as it puts a significant part of the preamp circuit, grounded to the chassis, when everything else, including the input jacks is grounded to the bus.

Clip the lead that grounds the pot leg and the resistor to the pot housing. Then solder a wire to that leg of the pot, leaving the resistor there as well. Solder the other end of the wire to the ground bus, with the wire as short as reasonably possible.

This may reduce noise a bit, and will eliminate some issues in the future in the event that the pot's lock-washer and chassis connection becomes oxidized, corroded, or loose.

Rob, another mod you might want to try, that I forgot to mention...

This is no huge deal, but I'm surprised that Gibson did this, as they are isolating the input jacks from the chassis. Notice how they grounded the one leg of the volume pot, to its housing using the lead of the resistor? I'm surprised they did this as it puts a significant part of the preamp circuit, grounded to the chassis, when everything else, including the input jacks is grounded to the bus.

Clip the lead that grounds the pot leg and the resistor to the pot housing. Then solder a wire to that leg of the pot, leaving the resistor there as well. Solder the other end of the wire to the ground bus, with the wire as short as reasonably possible.

This may reduce noise a bit, and will eliminate some issues in the future in the event that the pot's lock-washer and chassis connection becomes oxidized, corroded, or loose.

Yes, I did take notice of that as I was looking more closely at the chassis yesterday and wondering why they didn't route to the bus ground (so close by, too). I'm not a fan of those plastic housed Clif jacks and will eventually replace with Switchcrafts as well.

Yes, I did take notice of that as I was looking more closely at the chassis yesterday and wondering why they didn't route to the bus ground (so close by, too). I'm not a fan of those plastic housed Clif jacks and will eventually replace with Switchcrafts as well.

Yeah, I installed Switchcrafts, and grounded what is now the preamp buss to them.

I isolated the preamp ground buss from the power amp ground bus. Simply cutting the bus, between where the preamp filter cap and the grid filter cap are grounded does this.

http://www.specialtyguitars.com/images/ebay/ground.jpg

(This photo was taken before I re-did the volume pot ground)

With this, the power amp bus is grounded to the chassis at the power transformer, and the preamp bus is grounded to the chassis at the input jacks.

I can't say that this made a huge difference, but I figured it the way to go when I went to the Switchcraft input jacks.

From Radio Shack's website-

47K ohm 1/2W 5% Carbon Film Resistor pk/5
Model: 271-1130 | Catalog #: 271-1130
$0.99

If you have any problems getting them e-mail me your mailing address and I'll put one in the mail to you.


Thanks for the offer - picked up a set a little while ago - RS is about 8 blocks from here -

Are these resistors "directional"? Or is that a cap thing?

I love the mods. My GA-5 was made in 2oo1 and is slightly different than the ones I have seen in this thread. No metal screen or cord cubby, Metal Switchcraft inputs, and Sprague caps. Ifirst connected the 47k NFB r to pin#8 and recieved a good dose of squeal. After re reading the post, I connected to pin#3 and things were fine. You may have noticed that I also installed .1 coupling caps. I play harp with my GA-5 and the .1's give my amps a little more body. I seemed to see a resistor connected to pin#7 in the pic that showed the NFB mod by Specialty Guitars, What is it?
http://harmony.demont.net/myharmonies/Jaybird/GA_5mod2.jpg
http://harmony.demont.net/myharmonies/Jaybird/GA_5mod1.jpg

Thanks for the offer - picked up a set a little while ago - RS is about 8 blocks from here -

Are these resistors "directional"? Or is that a cap thing?

Nope, not polarized like an electrolytic cap.

After putting my amp partialy together, I ran a short bench test and dicovered a "motorboating" noise when the amp was turned all up. I disconnected the NFB mod and it went away. What might cause this? Resistor value?

After putting my amp partialy together, I ran a short bench test and dicovered a "motorboating" noise when the amp was turned all up. I disconnected the NFB mod and it went away. What might cause this? Resistor value?

When you first installed the NFB r to pin 8, are you SURE it was pin 8?

After putting my amp partialy together, I ran a short bench test and dicovered a "motorboating" noise when the amp was turned all up. I disconnected the NFB mod and it went away. What might cause this? Resistor value?

The NFB resistor should go to pin 8 of the 12AX7, which is the cathode of the second preamp stage. Pin 3 is the cathode of the first preamp stage which is all wrong.

If you want a "bigger" tone, you must jumper across the 22pF/1 meg low freq filter. It is negating anything your 1uF caps are doing.

And, if you are using a microphone (for harp) you need to install a 2.2M - 4.7M resistor from the #1 input hot to ground. Otherwise you will have runaway gain and feedback.

When I connect the NFB r to pin 8, There is a horrible squeal that happens as soon as the tubes warm up. I have jumped the 22pF/1 meg low freq filter. I will put in the 2.2M r from #1 input hot to ground and see how it goes.

Another available at $299 for the U.S. only!!

http://www.amazon.com/Gibson-Goldtone-Paul-Jr-Blonde/dp/B000LPUJX2/ref=sr_1_1?ie=UTF8&s=musical-instruments&qid=1205082658&sr=8-1

False alarm, my aploligies. Amazon has not been updated yet , as I phoned Giardinelli, and they have zero left.

When I connect the NFB r to pin 8, There is a horrible squeal that happens as soon as the tubes warm up. I have jumped the 22pF/1 meg low freq filter. I will put in the 2.2M r from #1 input hot to ground and see how it goes.


If I'm not mistaken, you said you had it on pin 7 in a previous post. Pin 8 (the correct pin) should cause no problems. The horrible squeal may be from using a mic with no input resistor.

No actually I had it on pin 8 and it sqealed without anything in the input. It began to squeal as soon as the amp warmed up. I did ask about what looked like a resistor going into pin 7 on the pic you posted of the NFB mod. Right now the 22pf ,1 megbypass along with the .1 caps and the amp is sounding pretty sweet. I just finished building a 5F1 tweed clone and they are both a lot alike. I think the 5F1 is a tad better for harp, A little more grit, or honk. The GA-5 has got the juice. Using them with a DD-3 delay and the sound is real full for both amps.

Earlier in this thread, someone had suggested that these amplifiers were imported.

I asked Gibson and have been told by them, in an e-mail, that these amplifiers were made in North Carolina. Mojotone is in North Carolina. Maybe that's why they have Mojotone components.
I have even heard it said, in this thread, I believe and on other wbsites, that Mojotone built these amplifiers for Gibson.

Earlier in this thread, someone had suggested that these amplifiers were imported.

I asked Gibson and have been told by them, in an e-mail, that these amplifiers were made in North Carolina. Mojotone is in North Carolina. Maybe that's why they have Mojotone components.
I have even heard it said, in this thread, I believe and on other wbsites, that Mojotone built these amplifiers for Gibson.

Makes sense, as the Mojotone website sells such items as Gibson Goldtone speakers and other components found in the amp. I never believed that they were imported - I even doubt that any of the components are imported.

So then....

How much would it cost to build this amp? Cab, speaker, caps, transformers etc.

So then....

How much would it cost to build this amp? Cab, speaker, caps, transformers etc.

Buying retail, much more than $300.

So then....

How much would it cost to build this amp? Cab, speaker, caps, transformers etc.

My guesstimate?

If you bought the parts individually and assembled it yourself:

$300 - if you are very lucky. :lol:

Chassis - 50
Trannys - 50
Speaker 30
Board resisters caps 25

that's 155

find a cabinet for 145 and you are in business . . . .

Or are my numbers above way off?

edit to note that RobDi beat me to it - and confirms that my guess is not as crazy as I thought. :cool:

and to fix math - again :oops::oops:

I even doubt that any of the components are imported.

Some components are definitely imported.
The Weber Signature speaker, for instance. I'm pretty sure it's imported.
The input jacks were made in the UK. Eastern European tubes, etc. They used to come with US made Sprague filter caps. Not anymore. Have you priced Sprague Atoms lately? They're not worth what they get for them.

Buying retail, much more than $300.

Mojotone gets over $500 for a tweed Champ kit. Weber, over $400.

Original '50s GA-5 amps can be had for less than $300, though.

In any case, these amps were a good deal.

Some components are definitely imported.
The Weber Signature speaker, for instance. I'm pretty sure it's imported.
The input jacks were made in the UK. Eastern European tubes, etc. They used to come with US made Sprague filter caps. Not anymore. Have you priced Sprague Atoms lately? They're not worth what they get for them.

The main speaker page at Weber's site says "Proudly Made In The USA", and he states that his speakers are hand built to order, so I never suspected that the speaker was imported - unless it is not actually a Weber product. I have always figured that the Epi version for the Valve Junior was a copy made in Asia. Mere speculation on all of this on my part - I don't really know :grin:

The main speaker page at Weber's site says "Proudly Made In The USA", and he states that his speakers are hand built to order, so I never suspected that the speaker was imported - unless it is not actually a Weber product. I have always figured that the Epi version for the Valve Junior was a copy made in Asia. Mere speculation on all of this on my part - I don't really know :grin:

It's the Weber Signature speakers that are imports - all the other Weber speakers are home built in their shop.

It's the Weber Signature speakers that are imports

Sounds good, though...

Get a load of this, MF has abandoned the six digit code that matches this product. That leads me to believe that when a new version arrives, it'll be a Mark II or whatever. And anyone's guess as to price.

Kinda mind boggling to ask for $ 699 and not bother to put a US source speaker in the amp. I guess people's awareness on this subject has changed a lot in the last 2 years.

Kinda mind boggling to ask for $ 699 and not bother to put a US source speaker in the amp.

My Mesa/Boogie cost twice that and has a Celestion speaker that was made in China. Very Few speakers are made here and when they are, they're too expensive to put in $699 amps.

No actually I had it on pin 8 and it sqealed without anything in the input. It began to squeal as soon as the amp warmed up. I did ask about what looked like a resistor going into pin 7 on the pic you posted of the NFB mod. Right now the 22pf ,1 megbypass along with the .1 caps and the amp is sounding pretty sweet. I just finished building a 5F1 tweed clone and they are both a lot alike. I think the 5F1 is a tad better for harp, A little more grit, or honk. The GA-5 has got the juice. Using them with a DD-3 delay and the sound is real full for both amps.

Yeah, that's the weirdest thing. It's a 1.5k resistor, that was installed by the factory. I haven't read where anyone else's GA5 has this. The only thing I can figure is that it was a mod they did, possibly due to instability caused by that high pass filter they're installing on these. Maybe some individual amps gave them trouble, and they installed this mod if needed. But I really don't know.

I removed the resistor, and the amp is louder (as expected) and a bit brighter, but still stable.

Yeah, that's the weirdest thing. It's a 1.5k resistor, that was installed by the factory. I haven't read where anyone else's GA5 has this. The only thing I can figure is that it was a mod they did, possibly due to instability caused by that high pass filter they're installing on these. Maybe some individual amps gave them trouble, and they installed this mod if needed. But I really don't know.

I removed the resistor, and the amp is louder (as expected) and a bit brighter, but still stable.

Mine has that 1.5k resistor on pin 7 too. I was surprised to see it there. It's not on the schematic that Gibson sent me.

So I can try it without it?

After playing my amp a while today, I decided that I like it better stock, so I reverted all the mods. I was never able to get that NFB resistor to function properly, The 25uf cap "leglift" just made the amp sound spotty and gargley, so now everything is stock except I left in the .1 coupling caps, I am really likeing the amp again. I sort of ABed it with my new 5F1 and they both are pretty sweet. I must say that I believe the 5F1 is a little richer sounding though. This is a great thread with some good ideas and timely responses.

Mine has that 1.5k resistor on pin 7 too. I was surprised to see it there. It's not on the schematic that Gibson sent me.

So I can try it without it?

I guess I can because I just did. It sounds fine, even cranked.

It's very slightly brighter and more open.

I sort of ABed it with my new 5F1 and they both are pretty sweet.

Sort of???

"Sort of", being a lazy way of saying aA/B'd. Sorry for the laxity. I ran them side by side , same mic, same setting, same song, same player. What can I say? To my ears, the 5F1 is a bit richer and has more body. The GA-5 has more muscle and volume, but not that suble little soul that is produced by a 6V6. The El84 is in my opinion a more volatile, dangerous, sound. I also used the line out in my 5F1 and ran them both together. Very cool. Mars and Venus holding hands.

So I can try it without it?

No. It may kill you! :twisted:

Seriously, give it a shot. Let me know if anything (good, bad, or ugly) happens.

Like any of this stuff, you can always put it back. :wink:

No. It may kill you! :twisted:

Seriously, give it a shot. Let me know if anything (good, bad, or ugly) happens.

Like any of this stuff, you can always put it back. :wink:

Good, because I already did it! See post #418!

Good, because I already did it! See post #418!

Right on.

I have never seem or heard of that being done with that grid resistor . I'd really like to know the scoop on that one.

After playing my amp a while today, I decided that I like it better stock, so I reverted all the mods. I was never able to get that NFB resistor to function properly, The 25uf cap "leglift" just made the amp sound spotty and gargley, so now everything is stock except I left in the .1 coupling caps, I am really likeing the amp again. I sort of ABed it with my new 5F1 and they both are pretty sweet. I must say that I believe the 5F1 is a little richer sounding though. This is a great thread with some good ideas and timely responses.

Yours is a unique one for sure. I can't imagine lifting that 25uF cap would make it sound "spotty and gargley", when all it does is reduce gain. NFB can be a tricky issue. I do wonder if the .1uF caps made it unstable. Yours is the only one that's had those problems (that we know of), and it's the only one with different value coupling caps. Amp circuits are kind of a "balancing act".

I had said that I liked this amp better than my fav 5F1 build. I take that back. It is more that it is louder and different, but not necessarily better. With the 5F1's solid pine cabinet, floating baffle board and other differences, it is more complex. The GA5 has it with more sparkle and loudness.

No here's one for you.

I replaced the Xicon filter caps with a two 20uF F&Ts and a 16uF Sprague Atom (preamp filter) basically just because I could. I would have used those 15uF Sprague Atoms if I had a source for them.

First thing I noticed was that the 60hz hum was greatly reduced. The second thing was that the amp sounds even better. More musical and responsive.

I hadn't given this any thought but it is claimed that electrolytics should be powered up at least once a year, otherwise they will not preform as well. My amp is a November 2006 model. So it is unlikely that, until the other day, it had not been powered up since it was final tested in 11/06 prior to being boxed up.

Some say Sprague Atoms are better than the imports electros, some say not. But I think it's very safe to say that this new Sprague and these new F&Ts are head and shoulders above the old Xicons I removed.

Yours is a unique one for sure. I can't imagine lifting that 25uF cap would make it sound "spotty and gargley", when all it does is reduce gain. NFB can be a tricky issue. I do wonder if the .1uF caps made it unstable. Yours is the only one that's had those problems (that we know of), and it's the only one with different value coupling caps. Amp circuits are kind of a "balancing act".

I had said that I liked this amp better than my fav 5F1 build. I take that back. It is more that it is louder and different, but not necessarily better. With the 5F1's solid pine cabinet, floating baffle board and other differences, it is more complex. The GA5 has it with more sparkle and loudness.

It is very possible that the .1 coupling caps have changed my circuit enough that your mods do not fit well in my amp. If that is so, then there are two ays to change the stock soundd of the GA-5


You are also right in pointing out the difference in cabinets between the GA-5 and 5F1. I believe that cab design has a ton to do with how the amp sounds. I think I may run my GA-5 through the 5F1 cabinet and see what happens. After all, the two circuits are not that different from each other, apart from the power tubes.

It is very possible that the .1 coupling caps have changed my circuit enough that your mods do not fit well in my amp. If that is so, then there are two ays to change the stock soundd of the GA-5


You are also right in pointing out the difference in cabinets between the GA-5 and 5F1. I believe that cab design has a ton to do with how the amp sounds. I think I may run my GA-5 through the 5F1 cabinet and see what happens. After all, the two circuits are not that different from each other, apart from the power tubes.

They're not really my mods. Removing the 22pF/1 meg high pass filter, and installing the NFB resistor, are simply making those parts of the circuit like the vintage GA5, which is similar to a 5F1.

Vintage GA5 http://www.gibson.com/Files/schematics/GA-5.pdf

New GA5 http://www.diycustomamps.com/images/schematics/gibson_ga5_schem.pdf

Removing the 25uF bypass cap on the first gain stage is making that part of the circuit like a 5F1 versus the 5E1 or GA5 in that part of the circuit.

5F1 http://www.ampwares.com/ffg/schem/champ_5f1_schem.gif

5E1 http://www.ampwares.com/ffg/schem/champ_5e1_schem.gif

So actually, those mods make the new GA5 circuit more like the 5F1 circuit.

Now all the GA-5 needs is a standby ... :cool:

No here's one for you.

I replaced the Xicon filter caps with a two 20uF F&Ts and a 16uF Sprague Atom (preamp filter) basically just because I could. I would have used those 15uF Sprague Atoms if I had a source for them.

First thing I noticed was that the 60hz hum was greatly reduced. The second thing was that the amp sounds even better. More musical and responsive.

I've been thinking about messing with the filter caps since getting this amp. Theschematic calls for 3 x 15uF, 3 x 22uF was used, a 5F3 Champ used 3 x 8uF and the original GA5 schematic calls for 1 x 20uF and 2 x 10uf.

Changing the first filter cap in my 5E3 clone to 30uF (from 16uF) tightened up the bass with the amp cranked quite a bit. Gerald Weber recommended not putting higher value filter caps in Champs. From what I've seen, filter cap values alter the looseness and tightness of an amp (as well as noise, of course) rather than tone.

It's a fairly cheap experiment to see how the amp responds to lower value filter caps.

I have a bunch of 16uF@475v caps including a Sprague Atom (will it fit in there???) that I can try in there. I'd be tempted to try 1 x 20uf and 2 x 10uF like the original schematic.

BTW, all of my recent 16uF Sprague Atoms measure 19uF on my capacitor meter.

Now all the GA-5 needs is a standby ... :cool:

Yes. I tried about a dozen old pre-amp tubes in mine this weekend and I'm afraid to leave one in the amp without a standby switch!

The amp sounded best with a Mullard and an old Amperex Bugle Boy. There was a lot of chime and sparkle with the Amperex.

Yes. I tried about a dozen old pre-amp tubes in mine this weekend and I'm afraid to leave one in the amp without a standby switch!


What problem or condition does the standby switch address? Is it because the power amp tubes are being run too hot? Because my expectation would be that tubes kept well within their rated operating parameters ought to have a very long life and make removing the plate voltage sort of overkill.

I've got a buncha 20uf 500v Atoms, BIG light blue cans - almost longer than the circuit board is wide!

I'll be wiring up the Carling 3-way off/standby/on today ...

http://img.photobucket.com/albums/v82/rfdee/standby2.jpg

What problem or condition does the standby switch address? Is it because the power amp tubes are being run too hot? Because my expectation would be that tubes kept well within their rated operating parameters ought to have a very long life and make removing the plate voltage sort of overkill.

The s/s rectifier slams the tubes with full voltage, the standby allows the heaters to warm up the tubes = longer tube life.

So it's the startup and not the time spent hot that matters. Gotcha.

On amps without a standby switch, then would it be best to turn it on and leave it on if you're going to be away for an hour or two? Seems like having fewer cold startups might be more important to tube life than avoid an extra hour of sitting around at idling at full steady-state plate voltage.

It looks like there's room to easily add a tone pot if you wanted. By the green wire.

http://img3.musiciansfriend.com/dbase/pics/products/7/3/8/265738.jpg

Is that the power transformer or the output transformer? Why do I see just one? And is it as tiny as it appears?

The 15 watt Fender Super Champ XD has much heftier transformers.

I'm not saying don't buy the Gibson. Just an observation.

Is that the power transformer or the output transformer? Why do I see just one? And is it as tiny as it appears?

Inside the chassis sits the OT, on the other side is the PT

The 15 watt Fender Super Champ XD has much heftier transformers.

As they should be, a GA-5 or Champ is 5 watts.

I'm not saying don't buy the Gibson. Just an observation.

Yer learning new stuff every day ..... like us all. :cool:



....

Is that the power transformer or the output transformer? Why do I see just one? And is it as tiny as it appears?

The 15 watt Fender Super Champ XD has much heftier transformers.

I'm not saying don't buy the Gibson. Just an observation.

That's the output transformer. The power transformer's underneath the chassis.

Those are made in USA Mojotone branded Heyboer transformers in the GA5. They're small because it's a 5 watt amp.

Who made the transformers in the Superchamp XD and where were they made?

That's the output transformer. The power transformer's underneath the chassis.

Those are made in USA Mojotone branded Heyboer transformers in the GA5. They're small because it's a 5 watt amp.

Who made the transformers in the Superchamp XD and where were they made?

My mistake. I was under the impression the Gibson is also 15 watts.

I just looked. The brand name on the ouput transformer is Chuang Meei and the model # is 0731. Made in Taiwan.

... I just looked. The brand name on the ouput transformer is Chuang Meei and the model # is 0731. Made in Taiwan.

As expected. :sad:

The GA-5 has Heyboer trannies. :cool:

I just started another thread on this....MF is selling "blems" for $230. I'm sure these are the returns. Here's a great opportunity for someone to pick one up for an even better deal.

http://www.musiciansfriend.com/product/Gibson-Goldtone-Les-Paul-Jr.-Amp?sku=481209X

I just started another thread on this....MF is selling "blems" for $230. I'm sure these are the returns. Here's a great opportunity for someone to pick one up for an even better deal.

http://www.musiciansfriend.com/product/Gibson-Goldtone-Les-Paul-Jr.-Amp?sku=481209X


Those are returns - I just knew that was gonna happen.

I've been thinking about messing with the filter caps since getting this amp. The schematic calls for 3 x 15uF, 3 x 22uF was used, a 5F3 Champ used 3 x 8uF and the original GA5 schematic calls for 1 x 20uF and 2 x 10uf.

Changing the first filter cap in my 5E3 clone to 30uF (from 16uF) tightened up the bass with the amp cranked quite a bit. Gerald Weber recommended not putting higher value filter caps in Champs. From what I've seen, filter cap values alter the looseness and tightness of an amp (as well as noise, of course) rather than tone.

It's a fairly cheap experiment to see how the amp responds to lower value filter caps.

I have a bunch of 16uF@475v caps including a Sprague Atom (will it fit in there???) that I can try in there. I'd be tempted to try 1 x 20uf and 2 x 10uF like the original schematic.

BTW, all of my recent 16uF Sprague Atoms measure 19uF on my capacitor meter.
Don't forget that there are many versions on the GA-5 about. The one discussed here has 22x22x22 which is pretty standard these days. Champs are different and do benefit from a 16x8x8 configuration and sound better with the early Princeton's 32x8x8 setup. Most EL84 amps actually have an extra 20 to 50 cap with a small resistor (~150R) before the first 3 caps. See attached schematic.

Also from memory the GA-5 has no 1M resistor from the input to ground. That was an error in the early Gibson schematics that got carried forward.

On amps without a standby switch, then would it be best to turn it on and leave it on if you're going to be away for an hour or two? Seems like having fewer cold startups might be more important to tube life than avoid an extra hour of sitting around at idling at full steady-state plate voltage.

No, that's not ideal either. Single ended amps such as this run the power tube full-on all the time, so you are wearing down your power tube by leaving the amp on when not in use, as you would be to a lesser extent with a push-pull amp as well.

So on balance if I'm going to play my little Champion 600 for an hour, then go eat dinner and watch TV for a couple hours and play for another 45 minutes before bed should I shut it down or leave it humming?

Also from memory the GA-5 has no 1M resistor from the input to ground. That was an error in the early Gibson schematics that got carried forward.

Not an error. When you plug your guitar in, it's resistance to ground takes the place of that grounding resistor. Gibson factored that in. As long as you are using a guitar, you're fine. If you plug in a mic for harmonica, it can cause big trouble with runaway gain.

So for harp players, a 4.7 meg resistor should be installed from the input to ground in vintage GA5s and in these new ones. For guitar, the input should be left as is.

Hey folks :)
I hate to bring this awesome discussion back to elementary level (but I am a first grade teacher!) Anyway, I've gotten all the goodies I need to do the 3 original electrical mods you talked about, but now I'm balking. Chalk it up to inexperience. Could you break those 3 down fer me? What effect can I expect for each one?

The lifted cap
The jumpered resistor (1m + 22pf cap)
The NFB

Again, sorry to be so elementary! I am in love with my amp as is, and now I realize I may be getting swept away with results I'm not even sure of!
Duh ;)

droo

Hey folks :)
I hate to bring this awesome discussion back to elementary level (but I am a first grade teacher!) Anyway, I've gotten all the goodies I need to do the 3 original electrical mods you talked about, but now I'm balking. Chalk it up to inexperience. Could you break those 3 down fer me? What effect can I expect for each one?

The lifted cap
The jumpered resistor (1m + 22pf cap)
The NFB

Again, sorry to be so elementary! I am in love with my amp as is, and now I realize I may be getting swept away with results I'm not even sure of!
Duh ;)

droo

If yer happy with the GA-5 as is, don't bother with any mods.

There is no way to fully describe what the trinity circuit mods will sound like for you - lots also depends on the kinda guitars/pickups you plug in, and what and how you play.

The trio of circuit mods will remove that shrill boxy tone, allow for a fuller 'n' fatter tone, greatly reduce hum ... this basically somewhat lessens the raunchy, overly trebly "tweed tone" to a more manageable level.

Just do all three at the same time, they compliment each other and they are way too easy to accomplish, OR to undo ...

The lifted cap - cut the jumper, as shown
The jumpered resistor (1m + 22pf cap) - solder a wire across those turret terminals, as shown
The NFB - add a 47k resistor from the yellow wire on the RCA jack to pin 8 of the 12AX7 socket, as shown

http://img.photobucket.com/albums/v82/rfdee/3circuitmods2.jpg

Rob, I'm waiting on you to post sound clips of your "modded" vs "unmodded" GA-5's. Since you've already done the mods (and like them) and have 2 amps, you're the logical choice to help some of us decide if we want to follow suit.

Not an error. When you plug your guitar in, it's resistance to ground takes the place of that grounding resistor. Gibson factored that in. As long as you are using a guitar, you're fine. If you plug in a mic for harmonica, it can cause big trouble with runaway gain.

What Gibson didn't factor in is new fangled stuff like effects pedals and tuners etc that all expect and work best with a 1M impedance.

Rob, I'm waiting on you to post sound clips of your "modded" vs "unmodded" GA-5's. Since you've already done the mods (and like them) and have 2 amps, you're the logical choice to help some of us decide if we want to follow suit.

Eventually I'll put up some sound bytes - but I will caution everyone that MY sound bytes have nothing to do with how an amp will sound for YOU with YOUR gear and YOUR playing.

Remember, the guitar tone path = brain, fingers, pickups, amalgam of the guitar, FX (if any), amp (circuit, tubes, speaker, etc).

I can't say this any other way - the trinity circuit mods are so easy and cheap to accomplish AND UNDO that you should just do them and see for yerself.

Thanks again Rob :) That last drawing is great!

I read this over on the FDP,

"They're back!!!!!!! Just got off the phone with Gibson, and news is MF has bought out all of the entire GA5 directly from Gibson. No other online vendors will have these in stock as confirmed directly by Gibson."

Interesting~droo

What Gibson didn't factor in is new fangled stuff like effects pedals and tuners etc that all expect and work best with a 1M impedance.

With effects and all that in line, it's all the same. The resistance to ground is still there, so the circuit is fine.

With all of the circuit changes, layout and other design differences, etc. between the vintage GA5 and this new one, the likelihood that the lack of a grid return resistor could be an accidental omission, carried over from the 50s to this new design, is less than infinitesimal.

I'm certain that Gibson knew about effects pedals and tuners when they designed this new model in 2002 or whenever it was.

[QUOTE=specialty guitars;1150915]Yours is a unique one for sure. I can't imagine lifting that 25uF cap would make it sound "spotty and gargley", when all it does is reduce gain. NFB can be a tricky issue. I do wonder if the .1uF caps made it unstable. Yours is the only one that's had those problems (that we know of), and it's the only one with different value coupling caps. Amp circuits are kind of a "balancing act".

I thought about this and decided to try some other value NFB resistor. First I used a 100k , because the squeal was so intense, I figured the 47k must be way off if what you told me is the case. There was still squeal, but not so immediate or scary sounding. Next I used a 1 meg resistor (overkill?) to just determine if anything stopped the squeal. No squeal, but no noticable difference in the amps sound. So now I think I will hook up a pot and see if I can dial in something. To your ears, just how does the NFB change the tone or sound of the amp, what should I be looking for?

With effects and all that in line, it's all the same. The resistance to ground is still there, so the circuit is fine.

With all of the circuit changes, layout and other design differences, etc. between the vintage GA5 and this new one, the likelihood that the lack of a grid return resistor could be an accidental omission, carried over from the 50s to this new design, is less than infinitesimal.

Strangely, Gibson did this on some amps but not others, i.e. the GA-6 had no pull down resistor yet the GA-40 and others did. The other advantage of having a 1M resistor in there is the improvement in signal to noise. It was how Leo did it and it is how everyone else still does it to this day and beyond.

Carling off/standby/on added.

I pulled the GA-5 2-way power switch and removed the brown wire that goes to the IEC socket and the twisted pair of black and black/white wires from the PT.

I moved those two wires over to the Carling switch (see diagram below).

I removed the short white jumper between the rectifier diodes and the first filter cap, replaced that with a twisted pair of 18 gauge stranded wires (red and green).

I connected the diode/filter wires to the Carling switch (see diagram below).

I installed the Carling switch so that the end without lugs faces up (flipped the switch around as it looks in the diagram below) - and bundled all the loose wires together with mini tie wraps.

The switch works flawlessly.

http://img.photobucket.com/albums/v82/rfdee/carling1.jpg

http://img.photobucket.com/albums/v82/rfdee/carling2.jpg

http://img.photobucket.com/albums/v82/rfdee/standby2.jpg

Where can u buy the carling switch ?

http://westlabs.com/Frames.HTML

DPTTP $ 9.00 Carling Super Heavy Duty

I thought about this and decided to try some other value NFB resistor. First I used a 100k , because the squeal was so intense, I figured the 47k must be way off if what you told me is the case. There was still squeal, but not so immediate or scary sounding. Next I used a 1 meg resistor (overkill?) to just determine if anything stopped the squeal. No squeal, but no noticable difference in the amps sound. So now I think I will hook up a pot and see if I can dial in something. To your ears, just how does the NFB change the tone or sound of the amp, what should I be looking for?

Again, something is not quite right with your amp. I believe the .1uF caps have made it unstable, and on the edge of parasitic oscillation. When you add the NFB resistor, it should not cause any problems, yet it does.

I can't say for sure without the amp in front of me, but my guess is that the .1uF cap installed between the second gain stage and the grid of the EL84 is causing the problem.

Until you get your amp under control, there is no point experimenting with NFB.

NFB smooths and evens out the frequency response. Early amps didn't have it at all. Tweeds acquired it, and blackface amps have more of it.

Less, or no NFB (high value resistor or none at all) makes the amp sound "raw". More NFB (lower value resistor) makes the amp sound more refined, with a more even response.

A common NFB resistor value for tweeds is 56K (some NFB). A common value for blackface amps is 820 ohms (a lot of NFB).

Carling off/standby/on added.

I pulled the GA-5 2-way power switch and removed the brown wire that goes to the IEC socket and the twisted pair of black and black/white wires from the PT.

I moved those two wires over to the Carling switch (see diagram below).

I removed the short white jumper between the rectifier diodes and the first filter cap, replaced that with a twisted pair of 18 gauge stranded wires (red and green).

I connected the diode/filter wires to the Carling switch (see diagram below).

I installed the Carling switch so that the end without lugs faces up (flipped the switch around as it looks in the diagram below) - and bundled all the loose wires together with mini tie wraps.

The switch works flawlessly.

http://img.photobucket.com/albums/v82/rfdee/carling1.jpg

http://img.photobucket.com/albums/v82/rfdee/carling2.jpg

http://img.photobucket.com/albums/v82/rfdee/standby2.jpg

Good job Rob. Excellent pics!

Ok so now that were talking about harmonicas, how would a harp player with a real Green Bullet get more headroom or "pre squeel" action out of a GA-5?

Even out on the end of a 25' cord, I cant even hit 12:00 without drilling out some ears!

Ok so now that were talking about harmonicas, how would a harp player with a real Green Bullet get more headroom or "pre squeel" action out of a GA-5?

Even out on the end of a 25' cord, I cant even hit 12:00 without drilling out some ears!

First, install a grid return resistor on the input. 4.7meg should work, you might have to go down to 2.2 meg or 1 meg.

Have you done any of the mods to it that are discussed on this thread?

First, install a grid return resistor on the input. 4.7meg should work, you might have to go down to 2.2 meg or 1 meg.

Have you done any of the mods to it that are discussed on this thread?

No, so far I'm just letting it sit on the floor and make friends with all the other animals.

I've only done the 10' HD computer cable mod which I thoroughly recommend if you can find one.

This is the best thread ever :cool:

This is the best thread ever

You're so right. I didn't realize, it isn't about whether I like this amp or need it. This is one fantastic tutorial for those with the time and a GA-5.

I'm wishing I could go to school, too. Just to learn more fundamentals here.

I got mine Monday. It says it was manufactured in June of 2006.

sooo, my question is.......If an amp sits around for so long without being played, doesn't that damage some of the components, or is that only if it sat idle for, say, 10 years....???

Just curious if this might be an "issue"

I got mine Monday. It says it was manufactured in June of 2006.

sooo, my question is.......If an amp sits around for so long without being played, doesn't that damage some of the components, or is that only if it sat idle for, say, 10 years....???

Just curious if this might be an "issue"

Quick answer - Nah.

Chances are extremely high that yer 2 year old GA-5 caps are just fine - mine from 2/06 were.

Most of the original GA-5 reissues came with Atoms for both the 1st and 2nd stage filters, but these later GA-5's aren't. So, if yer filter caps aren't Spragues, and you have some around or can get them cheap, you may be in for a sonic treat if ya stick'em in.

Modern electrolytic caps (since the late '50s, believe it or not) have a longer shelf life than earlier electrolytics.

This is why they don't typically need to be formed when istalled.

If you are concerned that 2 years is too long, you could form the caps before using the amp the first time.

Modern electrolytic caps (since the late '50s, believe it or not) have a longer shelf life than earlier electrolytics.

This is why they don't typically need to be formed when istalled.

If you are concerned that 2 years is too long, you could form the caps before using the amp the first time.

It could be that the Xicons in mine were at their best, and the Sprague Atoms are just better. Hard to say. The amp sounds much better with Sprague Atoms/F&Ts in it, the 60 hz hum was reduced, and that's that.

I may be accused of being a "cork sniffer" by some, but so be it. I am firmly in the camp that believes Sprague Atoms are better than the Asian made E caps. But, I gave the Xicons a fair shake, so as not to be accused, but I can say without a doubt that going to the Spragues and the F&Ts made noticeable improvements. Of course YMMV...

Where do you get physically small enough Sprague Atoms to use as filter caps in this amp?

Where do you get physically small enough Sprague Atoms to use as filter caps in this amp?

How about that electronics place on I-95 on the north side of Providence, RI?

Where do you get physically small enough Sprague Atoms to use as filter caps in this amp?

Who said they have to be small? :wink:

How about that electronics place on I-95 on the north side of Providence, RI?


Jabour Electronics, just of the highway in Pawtucket, RI? They closed a while back!

I know where to get Sprague Atoms, I have 2- 16uF@475v and a 30uF@500v in my 5E3 clone, it's just that they're freakin' huge, physically!!!

F&Ts aren't much smaller, some are bigger.

I was wondering where you'd get small enough Atoms to fit without jamming them in there, all goofy like.

Carling off/standby/on added.


I ordered my off/standby/on switch today!

The 20uf/500v Atoms are 2-1/4" long and 7/8" in diameter - they WILL fit on the GA-5 turret board. The 16UF/475v Atom for stage 1 is smaller at 1-5/8" long and 7/8" diameter. I'll be removing the 22uf IC caps out and soldering all the Atoms in. No big deal.

I was wondering where you'd get small enough Atoms to fit.

You're missing my point. They don't have to be small to fit. The 16uF Sprague Atom I used is the same as the ones you have. The 20uF F&Ts are only a little smaller, but are a better fit.

You just install them so they are above the turret lugs, so they are not touching anything.

http://www.specialtyguitars.com/images/ebay/filter.jpg

The F&Ts fit length-wise, but had to be skooched to the side a bit to make room for the Sprague.

You're missing my point. They don't have to be small to fit. The 16uF Sprague Atom I used is the same as the ones you have. The 20uF F&Ts are only a little smaller, but are a better fit.

You just install them so they are above the turret lugs, so they are not touching anything.

http://www.specialtyguitars.com/images/ebay/filter.jpg

The F&Ts fit length-wise, but had to be skooched to the side a bit to make room for the Sprague.

That doesn't look bad. I wasn't sure if they'd fit side by each because of the caps diameters.

That doesn't look bad. I wasn't sure if they'd fit side by each because of the caps diameters.

Well, the side by side thing can be dealt with. I thought about using 3 x Sprague Atom 20uF 500V. And it can be done, but the caps must be mounted up some, so that they can actually be place off to the sides a bit to make up for the diameters. There is a lot of usable "real estate" above the cathode bypass circuitry, and bit to the preamp side as well. It might not look as pretty, but as long as it is done properly, that wouldn't matter unless you have one of the clear plastic chassis models. :wink:

I've been reading all about this thing on the forums today, and that Blem at MF was in stock... up until about 2 minutes before I was going to purchase it. I tried to "add to cart", but it "has been discontinued". So somebody got the lucky $230 Blem at MF, and that's all she wrote... the GA-5's... ALL of them, are off MFs site, with no info whatsoever about their return. You can find the GA-5 page on MF if you google it, but it's not findable with MF search.

I've been reading all about this thing on the forums today, and that Blem at MF was in stock... up until about 2 minutes before I was going to purchase it. I tried to "add to cart", but it "has been discontinued". So somebody got the lucky $230 Blem at MF, and that's all she wrote... the GA-5's... ALL of them, are off MFs site, with no info whatsoever about their return. You can find the GA-5 page on MF if you google it, but it's not findable with MF search.

I do think they'll be back at MF and still selling at $299 ..... and if so, I'll buy a third one. :cool:

I do think they'll be back at MF and still selling at $299 ..... and if so, I'll buy a third one. :cool:

LOL...Rob, what are you trying to do, have a 10' x 10' wall of these things? :razz:

LOL...Rob, what are you trying to do, have a 10' x 10' wall of these things? :razz:

Hmmm, that would be cool. :cool: :roll:

Nah, give 'em to my kids and grandkids.

After looking at you pic, I took one of my amp, and they look to be the same. I removed all the mods I did to see if the NFB would work. It still squeals, to a whistle, when the tubes get warmed up. Crazy.

http://www.specialtyguitars.com/images/ebay/filter.jpg

I may just end up installing the .1 cap from the vol control. I did notice that after removing everything I did, that the amp did not seem as robust. I did leave the 4.5M resistor on the input.
http://harmony.demont.net/myharmonies/Jaybird/GA5new.jpg
http://harmony.demont.net/myharmonies/Jaybird/GA5new2.jpg

I tried to "add to cart", but it "has been discontinued". So somebody got the lucky $230 Blem at MF, and that's all she wrote.
The son of a woman I dated and convinced to buy one of these sent his back to MF on Tuesday. Said it wasn't "big enough". The tracking numbers say it will arrive there on Thursday.

I honestly don't think he played it more than 15 minutes so it will be in like-new condition. Keep an eye out if anyone still wants one. I don't know how many returns they get each day, but they probably get inspected within 1 or 2 days after arriving, then blem listed. Thur, Fri and Sat would be good days to be checking the link, if interested.

You may remember when we all started getting our amps delivered that I said that mine was real tight and brittle sounding and that I was disappointed. I've held my nose and played it everyday hoping it would open up. Well it did. Last night I noticed that it seemed to sound better. Tonight, it sounds a lot better. I really like it now. I don't know if it's finished breaking in or not but I could handle it if it just kept getting better for a few days. Now I see why all of you are having so much fun. What a deal.

On top of that, I brought home a brand new Gretsch 6118T Anniversary. It's the 2-tone smoky cadillac green. It really sounds great thru that little GA-5 amp. :grin:

Rob, I put in an input jack for the 8 ohm tap like you suggested. A pretty fast and simple deal. It now gives me more choices for speaker tweeks. I just slid in a nice old Magnavox AlNico that sounds pretty good. I am still trying to figure out why the NFB is a no go on my amp. When I sort that out I may do the rest od the three mods you talk about in such glowing terms.

Drill the chassis hole for the 1/4" jack ...
http://img.photobucket.com/albums/v82/rfdee/a6.jpg

Mount the wire the jack (oops, red lead is ground!) ...
http://img.photobucket.com/albums/v82/rfdee/a7.jpg[/QUOTE]

I am still trying to figure out why the NFB is a no go on my amp. When I sort that out I may do the rest od the three mods you talk about in such glowing terms.

Jay, as you pointed out, my amp is one of the ones that came with a 1.5k resistor mounted at the 12AX7 socket to the 2nd stage grid. These resistors were likely installed on amp that had trouble with parasitic oscillation.

So amps are more prone to that than others. It would seem that these amps can have problems with parasitics.

When you install the NFB resistor, it must be just enough to send yours over the edge.

Keep in mind, that I and Rob, did these mods one at a time, with the NFB resistor mod being the last one.

The order was:

1. high pass filter bypassed or removed

2. first stage bypass cap lifted or removed

3. install NFB resistor

It's possible, that the changes made by the first two mods, made the amp happier with the NFB when it was installed. I don't know. But I believe you were the only one of us who just did the NFB, without doing the others first. Is that correct?

Keep in mind, that I and Rob, did these mods one at a time, with the NFB resistor mod being the last one.

The order was:

1. high pass filter bypassed or removed

2. first stage bypass cap lifted or removed

3. install NFB resistor

It's possible, that the changes made by the first two mods, made the amp happier with the NFB when it was installed. I don't know. But I believe you were the only one of us who just did the NFB, without doing the others first. Is that correct?

I did my mods just like you two did. I figured that I wanted the high pass filter bypassed more than anything alse and wanted to do the mods one at a time so I could hear the difference.
I've had no problems with this amp whatsoever. The NFB resistor quited the amp down considerably.

I did my mods just like you two did. I figured that I wanted the high pass filter bypassed more than anything alse and wanted to do the mods one at a time so I could hear the difference.
I've had no problems with this amp whatsoever. The NFB resistor quited the amp down considerably.

That's right. I remember you saying that you knew the high pass filter had to go as soon as you saw it in the schematic, which was my thought as well.

It's hard to say why Jay's is acting like it is. Each amp is different. It could be that his wiper to grid wire is longer, running under the board, and coming through that hole in the board to get to the socket. Mine is making a straight shot from the wiper to the grid, above board. The shorter the better with grid wires.

But it's hard to know without the amp in front of you to check out.

I did the changes in the order that they were posted, so I guess that my amp just has some weird little gremlin that likes to squeal living under the board. Ha I have put a 12AT7 preamp tube in and will play it a bit this morning to see how it affects my tone and overall sound. I will probably reinstall the .1 cap off of the volume pot to the reamp as well as remove the 22pf bypass cap and give it a test ride. Your help and suggestions are greatly appreciated.

I did the changes in the order that they were posted, so I guess that my amp just has some weird little gremlin that likes to squeal living under the board. Ha I have put a 12AT7 preamp tube in and will play it a bit this morning to see how it affects my tone and overall sound. I will probably reinstall the .1 cap off of the volume pot to the reamp as well as remove the 22pf bypass cap and give it a test ride. Your help and suggestions are greatly appreciated.

You might consider replacing the signal lead off the vol pot to the preamp socket with a shielded lead.

You might consider replacing the signal lead off the vol pot to the preamp socket with a shielded lead.

Would that be the wire that leads to the pin(center on the pot) or the one that goes to the resistor(right on the pot)?

Would that be the wire that leads to the pin(center on the pot) or the one that goes to the resistor(right on the pot)?

Center wiper lug on the pot to preamp socket.

http://img.photobucket.com/albums/v82/rfdee/mods12.jpg

Tyhanks Rob. Mine is buried under the board, so It will have to wait until I have some extra time. Got to slide off to work. Thanks for the help.

I've noticed that Jay's amp is a little different than our new ones.

Not everything in our amps match Gibson's schematic. It scould be that changes were made over time to these that were not shown on the available schematic.

Things that work on the latest rev. might cause problems on an earlier rev., especially if things were done to make these amps more stable in recent revs.

You might consider replacing the signal lead off the vol pot to the preamp socket with a shielded lead.

+1

First, loosen the volume pot nut, reposition the lock washer, and re-tighten etc. It's imperative that the pot be making excellent contact with the chassis to be properly grounded.

Only ground the wire's shield at one end, the back of the volume pot would be the easiest.

Hey Rob. For the man who has a wall of tricked out GA5s, I think I know your next step. You should outfit them with Tone Tubby 8" speakers! :grin:

I just want to explain that when you sub lower gain tube like a 12AT7, it lowers the gain of the first stage, which is exactly what needs to be done to get a "clearer" tone with more headroom. Problem is, it also lowers the gain, or "cripples" the second stage, which was fine already with a 12AX7.

Simply lifting the lead on the 25uF bypass cap on the first stage, removes it from the circuit, which reduces its gain to an appropriate level with a 12AX7, so that the second stage is not effected.

I've been rereading all these great posts, and I wanted to ask what you meant by "crippling" the second stage with a lower gain tube like I had done. How's that translate in layman's terms ;) I'm new to the world of amp tweaking, and I ain't too educated on it...yet :)
droo

Ooh, ooh! I think I know this one...

The 12AX7 is a dual triode and as such provides the first two stages of gain to the amp. So if you switch from a tube with 100 units of gain to one with 70 units of gain, you don't reduce the gain by 30% but by 50% because the two are in series. Actually, in a real-world circuit the gain isn't equal to the spec that we're treating as "gain" but still the reduction is double what you'd think.

So if the first stage is distorting a little too early but the second stage is working just right, by subbing a lower-gain dual triode you could easily make it impossible for the second stage to do its job. I'm not sure what the second stage is supposed to do, it would seem to me that it is in fact the place that preamp distortion ought to happen since the levels it sees are 10, 12, 15dB higher than the input to the first stage. So maybe that's the "crippling".

OK guys, did I come anywhere close?

Jaybird: try reversing the OT leads-I've had the squealing problem on a new build and that fixed it.

Jaybird: try reversing the OT leads-I've had the squealing problem on a new build and that fixed it.
That's just what I was going to suggest...maybe the OT primary wire colors (or the secondary) were wrong from the factory (wouldn't be the first time), and with no NFB originally, it would not be detected as a problem at the factory...