$299 Gibson tube amp - Made in USA!

[zero2sixty]

Originally Posted by specialty guitars

That's fairly easy.

First, do not do any of the "trinity mods".

Second, turn on the amp's power switch.

Third, find the black knob on the chassis marked "Volume" and turn it fully clockwise...

Very nice! Humbuckers really kick out the lows...do you have any sound clip from your 30/16/8 cap mod that you did...sounds like that might help?

[Sevan Simonian]

No worries "Specialty Guitars", I got your meaning :)

But I really DO want to make sure I don't become "that guy" who takes this thread tooo far off topic.

Androo, I'll be sure to post feedback on the CVA8, but I'm a good 2-3 weeks away from having it in my GA5.

[Gee]

Originally Posted by zero2sixty

GEE, you hit the nail on the head. ...

I have found that by putting a Maxon OD-9 Pro in front of the GA-5, I can dial in the lead gain tone that I am looking for! I know that even that statement will draw a "face scrunch" from those that do not believe in using external effects...but instead of sending me back to the trinity mods (they are great ideas), anyone have any ideas on how to get my GA-5 to acheive that tone by performing internal mods so that I don't have to plug into a Moaxon OD-9 pedal?

I would like to preserve the integrity of this amp for its stock value but if there is a series of mods that will help me acheive the tone that I am looking for which will result in me keeping this little gem for the 20 years that it will take for it to become a "vintage" collectable, then it might be worth getting into the guts of the amp and tooling around.

See my post 243 earlier in this thread.

If the OD-9 gets you to where you want to be you need to tune the amp for more gain.
The following should achieve that:
1. Rewire the i/p jacks correctly to fix the lack of 1M ground reference. If you need a high low then copy any Fender Hi Lo layout (see picture below) otherwise put a 1M on the single i/p jack and use something like a 10K to loose any radio interference.
2. Replace the 2 1M resistors (R6 & R7) in the schematic in post 243 with 100Ks.
3. Replace the Plate resistors R3 & R4 with 100K. Nothing wrong with the 220K value but the 100K values make it easier to know the cathode resistor values that are tried and tested.
4. Reduce C3 to 2.2uF for single coils, 1uF for humbuckers.
5. Add C4 and try 2.2uF - big gain boost so can be put onto a switch.
6. Change R8 to 1.5K and R9 to 820 for 680 for even more crunch - big gain boost.
7. Change C5 to 1000-2000uF (25V or greater) - smooths out the distortion.
8. Add a grid stopper i.e. R15 1.5K to cancel any block distortion that be present.

The ratio of the plate resistors (R3 & R4) to the cathode resistors (R8 & R9) is important so that the pre amp is allowed to breath without being constricted and sounding harsh and fizzy.

See the Marshall schematic at the SEWATT VJ FAQ for more info. Those reversible changes should get you to where you want to be. I would suggest doing them one by one and listening to the amp so that you can fine tune it to get the distortion you want. You may or may not need all the mods - try it.

You make a good point about preserving the amp for 20 years. Just keep all the components you remove and they can be put back when you sell it or pass it on. Another thing worth doing would be to replace all the resistors with carbon film resistors - less noisy.

[red57strat]

Originally Posted by Guitar_Mc

I wonder how much of that was due to the impedence mismatch.

All of it, I'd guess. I've had the same result with a Champ and a different 8 ohm speaker.

I'll try my 8 ohm 12" Eminence Tonker with the amp this weekend and see if the result is similar. I'm sure it will be.

The real test would be to use the 8 ohm tap, but I don't even plan to pull the heat shrink tubing off of that.

[Guitar_Mc]

Originally Posted by red57strat

All of it, I'd guess. I've had the same result with a Champ and a different 8 ohm speaker.

I'll try my 8 ohm 12" Eminence Tonker with the amp this weekend and see if the result is similar. I'm sure it will be.

The real test would be to use the 8 ohm tap, but I don't even plan to pull the heat shrink tubing off of that.

Well, my other 8" Weber alnico speaker that I thought about trying is 8 ohm. So if I get around to trying it out, that heat shrink tubing is coming off mine.

It would make it more useful to me anyway since all my other amps and my 212 cab are all 8 ohm.

(Then again, I've got it sounding how I like it with the original speaker, so why mess with it?)

[Rob DiStefano]

Originally Posted by Guitar_Mc

Well, my other 8" Weber alnico speaker that I thought about trying is 8 ohm. So if I get around to trying it out, that heat shrink tubing is coming off mine.

It would make it more useful to me anyway since all my other amps and my 212 cab are all 8 ohm.

(Then again, I've got it sounding how I like it with the original speaker, so why mess with it?)

It'd make sense to allow for the 8ohm OT tap on the GA5 if those are the prime speakers you'll be using. Or better yet - drill a 1/4" hole in the chassis bottom, near the RCA jack, replace the RCA jack with a 1/4" Switchcraft jack, screw in a SPDT mini switch to the new 1/4" hole ya just drilled, wire the middle terminal on the switch to the hot side of the Switchcraft jack, wire the yellow OT hot wire to one side of the SPDT switch and the green OT hot wire to the other side of the switch, now you can select either 4 or 8 ohms output to the jack.

[Guitar_Mc]

Originally Posted by Rob DiStefano

It'd make sense to allow for the 8ohm OT tap on the GA5 if those are the prime speakers you'll be using. Or better yet - drill a 1/4" hole in the chassis bottom, near the RCA jack, replace the RCA jack with a 1/4" Switchcraft jack, screw in a SPDT mini switch to the new 1/4" hole ya just drilled, wire the middle terminal on the switch to the hot side of the Switchcraft jack, wire the yellow OT hot wire to one side of the SPDT switch and the green OT hot wire to the other side of the switch, now you can select either 4 or 8 ohms output to the jack.

I'm not big on drilling new holes in the chassis.

My thought was to switch the existing jack to the 8 ohm tap if I end up liking the 8 ohm 8" alnico speaker in there, then I can use an adapter if I want to run any of my other 8 om setups.

I just don't know if I'd like the alnico better than the stock one that is in there. Right now, I just put a mic on the amp and mix it in with my vocals in my 400W powered cab, so I don't really need to push any other speakers. My desire to push the other speakers, is just to see how it sounds through my other speakers when the impedence is matched.

I've also got a Weber minimass that somehow "magically" corrects the impedence for you if you want to try out different speaker impedences. I've never seen a schematic of the minimass though so I'm not exactly sure how that would work if the minimass volume is all the way up (no attenuation).

[Guitarslinger1]

Originally Posted by zero2sixty

Very nice! Humbuckers really kick out the lows...do you have any sound clip from your 30/16/8 cap mod that you did...sounds like that might help?

Thought you might like that.

Sorry, no clips. I downloaded some free program to record, and bought a condenser mic of some sort thinking it would be better than my old SM58s, and tried like hell to to record an amp demo track. Everything we did sounded LAME city. I kind of got discouraged after a few tries and shelved the idea.

I have several buddies with recording setups, but due to schedules and Murphy, it never seems to fall into place.

I still haven't decided n the filter caps. The preamp cap possible has the most noticeable effect. In general terms, the higher the value, the less bass and dynamics, with a more flat sound. The lower the value, the more bass, faster response and dynamics, and the treble can become a bit raspy. I have to agree with Rob that though the response with an 8uF in the preamp is very dynamic, the treble does become a bit raspy. So I'm kind of stuck between 10uF and 16uF, though 16uF seems kind of flat.

Of course, YMMV.

[Rob DiStefano]

Right now, the 22/16/10 Atom lineup works best of all for my main GA5, considering the guitars I use (Teles and Strats) and how I play (mostly fingerstyle) and what I play (an eclectic potpourri of bluez and jazz and "world age").

[Guitarslinger1]

Originally Posted by Rob DiStefano

...an eclectic potpourri...

Wow! You use your tongue prettier than a $20 ... Oops I can't say that here!

[zero2sixty]

Originally Posted by Gee

See my post 243 earlier in this thread.

If the OD-9 gets you to where you want to be you need to tune the amp for more gain.
The following should achieve that:
1. Rewire the i/p jacks correctly to fix the lack of 1M ground reference. If you need a high low then copy any Fender Hi Lo layout (see picture below) otherwise put a 1M on the single i/p jack and use something like a 10K to loose any radio interference.
2. Replace the 2 1M resistors (R6 & R7) in the schematic in post 243 with 100Ks.
3. Replace the Plate resistors R3 & R4 with 100K. Nothing wrong with the 220K value but the 100K values make it easier to know the cathode resistor values that are tried and tested.
4. Reduce C3 to 2.2uF for single coils, 1uF for humbuckers.
5. Add C4 and try 2.2uF - big gain boost so can be put onto a switch.
6. Change R8 to 1.5K and R9 to 820 for 680 for even more crunch - big gain boost.
7. Change C5 to 1000-2000uF (25V or greater) - smooths out the distortion.
8. Add a grid stopper i.e. R15 1.5K to cancel any block distortion that be present.

The ratio of the plate resistors (R3 & R4) to the cathode resistors (R8 & R9) is important so that the pre amp is allowed to breath without being constricted and sounding harsh and fizzy.

See the Marshall schematic at the SEWATT VJ FAQ for more info. Those reversible changes should get you to where you want to be. I would suggest doing them one by one and listening to the amp so that you can fine tune it to get the distortion you want. You may or may not need all the mods - try it.

You make a good point about preserving the amp for 20 years. Just keep all the components you remove and they can be put back when you sell it or pass it on. Another thing worth doing would be to replace all the resistors with carbon film resistors - less noisy.

Wow, that is great info. I think I may be over my head without following this via photos as most of my amp teaking experience has come from the insite and photo directions posted on this site. I'll open my amp up, grab the schematic and your notes and try to figure it out before I put the iron to it! I'll check out the other thread too. Thanks a lot!

[red57strat]

Originally Posted by zero2sixty

Wow, that is great info. I think I may be over my head without following this via photos as most of my amp teaking experience has come from the insite and photo directions posted on this site. I'll open my amp up, grab the schematic and your notes and try to figure it out before I put the iron to it! I'll check out the other thread too. Thanks a lot!

Remember to discharge the caps before poking around in there!

[zero2sixty]

How do you add an additonal cap and resistor?

[Rob DiStefano]

Originally Posted by zero2sixty

How do you add an additonal cap and resistor?

Where, what values and why?

[zero2sixty]

Sorry Rob, I was replying to Gee's post suggesting adding a cap and resistor, I don't know what he means.

[Rob DiStefano]

Originally Posted by zero2sixty

Sorry Rob, I was replying to Gee's post suggesting adding a cap and resistor, I don't know what he means.

Neither do I.

[guit30]

Coupons -music123 is taking eightyrocks -15%, They are tiny amps, about the size of the Fender Champion 600, saw 2 together @ Cintiollis in Philly
Jim

[Rob DiStefano]

Originally Posted by guit30

Coupons -music123 is taking eightyrocks -15%, They are tiny amps, about the size of the Fender Champion 600, saw 2 together @ Cintiollis in Philly
Jim

Yeah, I know about the 15% off thingy, but what amp are you talking about and why post it here on the GA5 thread?

[mchet]

Originally Posted by Rob DiStefano

Yeah, I know about the 15% off thingy, but what amp are you talking about and why post it here on the GA5 thread?

SURVEY SAYS!!!!

NONE

there are no amps on the discount list.

[Sidney Vicious]

Check out these detailed pics of the plexiglas version.

Somebody will save these for posterity, no doubt.

http://cgi.ebay.com/Gibson-Les-Paul-...QQcmdZViewItem

[androo]

It's just the weirdest looking amp ever, eh? See through?? Really??

On another note, I've been spending time a/b'ing my GA5 with my Peavey DB115. I gotta say...of course, there is waaaay more low end and volume on the DB. But tone-wise, no contest. This little bugger SMOKES it on pure tone. And the volume ain't that too far off either. Most gigs, I check my volume pot at the end of the night,and it's on 3 or 4 on the DB, everytime. When I put it on 3 or 4 in the studio, and crank up the Gibson too, the volume difference is not too noticeable. What's much more noticeable is the difference in quality tone. I might have to get rid of the DB altogether and maybe pick up another small wattage amp to go side by side at gigs. Something different, but low wattage.

Any ideas? Pro Jr? Blackheart? Any?

droo

[Gee]

Originally Posted by zero2sixty

How do you add an additonal cap and resistor?

Specifically which resistor and which cap?

With a board such as the one used in the GA-5 you can solder and re-solder the turret (silver posts) many times. So to remove a component, unsolder one end and when the solder is melted you need to pull the component lead away from the post. Then do the same to the other end of the component.