AA764 Help!

Hey all!

It's been some time, but I have been here, just not posting much. In fact, I've been here at Shock Brothers a LOT, trying to find info about getting a Triode AA764 Vibro Champ working... to no avail :(

I had a Fender Japan SS amp with twin 8" speaker that sounded meh, so I am using as my donor (recipient?).

After putting it all together, I have sound. YAY! But not good, in fact pretty unusable. Basically, treble and bass pots seem to be doing their thing, and speed does it's thing when the vibrato plug is shorted, which is how it's supposed to work. So I have volume and intensity pots that seem to be messing with one another, even when the vibrato is off. When vibrato is on (shorted), the intensity seems to work a few places in the sweep, then cause volume variations, then not affect intensity at all. the volume sweep is also spotty, and at the end of the sweep cuts out vibrato altogether.

This is my first build, and I'm happy to get any sound at all, but... :oops:

I have checked everything that I can with a cheapo multimeter, and all the resistors check out to spec. Everything is grounded properly (I think). All the solder points seem to be solid. What am I missing?!?! :confused:

Here's my Flickr set that shows all the steps I've taken, including tearing out the board and re-connecting everything, and changing pot locations to be in sinc with the Triode layout and the original Fender schematic. My Triode tech seems flummoxed, which is not a good sign. Please help!

http://http://www.flickr.com/photos/charisjapan/sets/72157629267256750


http://farm8.staticflickr.com/7211/6880427624_2c7135c58c_o.jpg (http://www.flickr.com/photos/charisjapan/6880427624/)
RCS_1699 (http://www.flickr.com/photos/charisjapan/6880427624/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

http://farm8.staticflickr.com/7081/7022658935_c268015080_o.jpg (http://www.flickr.com/photos/charisjapan/7022658935/)
RCS_1686 (http://www.flickr.com/photos/charisjapan/7022658935/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

http://farm8.staticflickr.com/7272/7022658359_5178eed7d8_o.jpg (http://www.flickr.com/photos/charisjapan/7022658359/)
RCS_1669 (http://www.flickr.com/photos/charisjapan/7022658359/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

Chris, ambitious. Odd layout to look at, though. I am going to think that there might be some problems with induced noise due to the lead dress. I don't know if that lead dress arrangement could have anything to do with how your trem function is working, but from my point of view things should be laid out differently. I would have put the pots and input jacks on the front panel. Things would be a lot simpler to 'see' and work on if it were laid out more like a FEnder VibrChamp...even if the lead dress as it is does not have deleterious effects on the fucntioins and the sonics.

Anyway....what are your voltages? Be aware that that bias vary trem circuit functions in connection with the cathode bypass circuit on that PI...and that bias point can have an affect on how the trem circuit functions. Lots of things to suspect....but voltages tell one a lot. Both 12AX7's are suspect...and this is an easy thing to change out to see if things change, right? But...check voltages first. NOte: bad tubes can cause voltages to be improper. All caps and resitors in the circuit are suspect. All connections are suspect. The pots are suspect. Step by step,......eliminate possible problems.
Do not accept that your work is correct. IT is also suspect. Ignoring this is a that is a trap that can prevent one from finding an error.
IN fact, I would suggest rebuilding the amp with the controls and input jacks on the front panel and leave the tube socket where they are...at the back.
This would at the least simplifiy any work...now and in the future. At best, this would eliminate some induced problems connected to the sloppy lead dress..

I say this with best of intentions. Good luck with it.

Have you tried just disconnecting the trem/vibro circuit to check that the volume issue goes away - at least then you might isolate the problems to the specific circuit involved in the vibro/trem. The use of the cascaded caps. is a bit tricky at times and does not always perform as speced.

Chris, ambitious. Odd layout to look at, though. I am going to think that there might be some problems with induced noise due to the lead dress. I don't know if that lead dress arrangement could have anything to do with how your trem function is working, but from my point of view things should be laid out differently. I would have put the pots and input jacks on the front panel. Things would be a lot simpler to 'see' and work on if it were laid out more like a FEnder VibrChamp...even if the lead dress as it is does not have deleterious effects on the fucntioins and the sonics.

Anyway....what are your voltages? Be aware that that bias vary trem circuit functions in connection with the cathode bypass circuit on that PI...and that bias point can have an affect on how the trem circuit functions. Lots of things to suspect....but voltages tell one a lot. Both 12AX7's are suspect...and this is an easy thing to change out to see if things change, right? But...check voltages first. NOte: bad tubes can cause voltages to be improper. All caps and resitors in the circuit are suspect. All connections are suspect. The pots are suspect. Step by step,......eliminate possible problems.
Do not accept that your work is correct. IT is also suspect. Ignoring this is a that is a trap that can prevent one from finding an error.
IN fact, I would suggest rebuilding the amp with the controls and input jacks on the front panel and leave the tube socket where they are...at the back.
This would at the least simplifiy any work...now and in the future. At best, this would eliminate some induced problems connected to the sloppy lead dress..

I say this with best of intentions. Good luck with it.

Wally,

Thanks a lot for the reply. Hehe! I assume good intentions here, unless I have a LOT of evidence to the contrary. :wink:

Yeah, I know my lead dress leaves a lot to be desired, and that the unconventional layout is certainly a potential problem. My explanation (excuse) is that none of the VC controls would match the labels on the front panel. (dumb reason) I thought that I could first do everything on the back just to get started, then mayeb get a new panel made... Until I found out how much a custom-size, custom labeled panel would cost! Anyway, to fix that, I plan to order a chassis with plate from Ceriatone. They're close to Japan (Malaysia) and the white is pretty! It won't fit in this combo, but I'll just make a head, and plug it in.

I will get those voltages and post. I did it twice before, but was very ignorant as to what I was doing, and they were weird, user error. I've since studied a bit here and other places, and think I can get reasonably accurate numbers now.

I'll try out different tubes (they just arrived) and measure again. I came to the conclusion that everything is suspect... especially ME! :oops:

I checked resistors (easy) and continuity as best I could understand. I have no clue how to check pots or caps, and my little multimeter is probably not much good for anything but VDC VAC and Ohms. Any suggestions?

Anyway, I really do appreciate your input, and want to get this thing singing! :smile:

Have you tried just disconnecting the trem/vibro circuit to check that the volume issue goes away - at least then you might isolate the problems to the specific circuit involved in the vibro/trem. The use of the cascaded caps. is a bit tricky at times and does not always perform as speced.

Hey, icd, thanks for your reply.

I responded to Wally's post, and will measure and post voltages and switch tubes as per his advice.

Please bear with this Noob! I'm a carpenter at best, a reasonably good mechanic, a 15-years-ago PC-tech, and play very bad guitar. A few months ago, I wouldn't have a clue what 'cascaded caps' meant, and even 'circuit' would be a bit vague. :oops: For your suggestion, I need some clarification, but I understand the concept (I think). A buddy told me that an AA764 was basically 'paint-by-numbers.' So (with apologies to Triode) I put numbers on their board layout. Where would I disconnect to isolate the trem? (my guess would be turrets 16, 18, 21, 23, and possibly the wire between pin 6 of the second AX7 and pin 4 of the 6V6?) Forgive a stupid question, but could you just pull the second AX7 tube?

OK, enough guessing on my part! :confused:


http://farm8.staticflickr.com/7227/6884877194_bacf260a25_o.jpg (http://www.flickr.com/photos/charisjapan/6884877194/)
Triode AA764 Vibro Champ 40-18027 120V Numbered (http://www.flickr.com/photos/charisjapan/6884877194/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

Pulling the 12AX7 would be the easiest 1st step to try. Second step would also to be to remove the yellow wire from the "intensity" pot - tape the end and keep it out of contact with anything else. Looking at the schematic, that should isolate the trem/verb part of the circuit. I am no expert on this type of trem/verb circuit, but I think that there is a little art as well as engineering involved as it relies upon controlled instability to give the effect. Thus it can be sensitive to voltages, lead dress and tolerance of components. However the issues you report seem more like engineering problems. Let us know how you get on. WATCH OUT FOR SMOOTHING CAP VOLTAGE RETENTION - DRAIN THOSE CAPS !

I guess you have done it more then once, but check each and every component value against the schematic and check each and every wiring connection just to be sure the circuit is as designed. No need to disconnect anything but just eyeball and checkoff against the circuit each element. Good luck !

Wally - voltages with volume,treble,bass at "5" (12 o'clock)

5Y3GT
2 - 348V
4 - 281AC
6 - 281AC
8 - 346V

6V6GT
3 - 346V
4 - 329V
5 - -3.0 at "0" +105mV, at "10" -7V
8 - 17.57V at "0" 20V, at "10" 16V

V2 AX7 (Vibro)
1 - 162.4V
2 - 0.4mV
3 - 1.539V
6 - 328V
7 - 162.8V
8 - 165.8V

V1 AX7 (Preamp)
1 - 205V
2 - 0.0
3 - 1.495V
6 - 204V
7 - 0.0
8 - 1.462V

And yeah, a 'proper' VC chassis would be best for lead dress. I have to admit that I'm not too thrilled about taking it all apart (again) and drilling out the front panel for these inch pots and working in those tight spaces. (sigh)

icd - I pulled the V2 tube. While the weird tremolo stuf is gone, the sound is still pretty bad, with strange oscillations through the volume sweep. It's a bit louder now, but not pleasantly so. Even at 12 o'clock, any kind of pick attack makes harsh sounds with pops and rude noise. At 3 o'clock it's just loud noise. I pulled the yellow intensity, no change. I switched the AX7s around, no change. Next I can try all new tubes, but that doesn't appear to be the problem. To test the speakers, I hooked up my Champ 600, that sounds great! Switched out the 6V6, and there was no change.

So... do you think it sounds reasonable to say that it's not the tremolo circuit causing the problem, but it DOES make whatever it is worse? Which brings me back to bad chassis layout/lead dress. Or do those voltages tell another tale? I've looked over the board and all the connections pretty carefully, and I'm pretty sure that the ground is correct.

Finally, I hear ya about scary caps!! :shock: As a carpenter/electrician, I've been knocked on my can a few times, and don't need THAT kind of 'inspiration.' ;)

Thanks so much for your help. charisjapan

Unless someone else corrects me, I think those voltages look close enough to the specs to be fine, I can't see an immediate problem there..

You could try disconnecting the negative feedback link. That's the wire that runs from the speaker connector to 2.7K resistor on the turret board. If the sound improves, then it is likely that the OP transformer is wired backwards. It won't hurt to run without the -ve feedback, but of course tape the loose wire to keep it safe.

IN fact, I would suggest rebuilding the amp with the controls and input jacks on the front panel and leave the tube socket where they are...at the back.
This would at the least simplifiy any work...now and in the future. At best, this would eliminate some induced problems connected to the sloppy lead dress..

I say this with best of intentions. Good luck with it.

Wally,

The way of a fool is right in his own eyes,
But a wise man is he who listens to counsel.

Thank you for good advice. I listened, I learned, I now hear sweet sounds! :grin:

And icd, thanks for the encouragement.

For the life of me, I can't find any difference in the connections, but now I have a wonderfully tubey amp! Switched things around closer to the original Fender layout, snipped about 3 feet of extranaeous wire, and added the power cable socket. Dimed guitar + dimed amp = a LOUD 5W! And man, the "vibro" (tremolo) is excellent.

One little thing... When Vibro is not engaged, the Intensity pot turns down the volume at the end of the sweep. Not completely, but definitely affects the volume of the amp. Anyone?

Btw, a few pics:

http://farm8.staticflickr.com/7049/7049892471_36116fab89_o.jpg (http://www.flickr.com/photos/charisjapan/7049892471/)
RCS_1841 (http://www.flickr.com/photos/charisjapan/7049892471/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

http://farm8.staticflickr.com/7213/7049892569_584ff57892_o.jpg (http://www.flickr.com/photos/charisjapan/7049892569/)
RCS_1845 (http://www.flickr.com/photos/charisjapan/7049892569/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

http://farm8.staticflickr.com/7110/6903802554_85c0766808_o.jpg (http://www.flickr.com/photos/charisjapan/6903802554/)
RCS_1852 (http://www.flickr.com/photos/charisjapan/6903802554/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

http://farm6.staticflickr.com/5340/7049892889_538de21a23_o.jpg (http://www.flickr.com/photos/charisjapan/7049892889/)
RCS_1862 (http://www.flickr.com/photos/charisjapan/7049892889/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

Great, I'm glad you solved it. I'm afraid that I can shed no light on the volume issue.

Great, I'm glad you solved it. I'm afraid that I can shed no light on the volume issue.

I wish I could credit myself with solving it.:wink: But it sure looks better than the 'spaghetti mess' before!

As to the volume/intensity connection, I can't see anything in the layout that would make them interact!:?: However, it only happens when the Vibro is disengaged, and I'm finding that I like it on all the time. With intensity at '0' it's completely transparent, and doesn't make any real tremolo until 11 0'clock or so. From there it's got a nice taper all the way to a very strong effect.

Best part is, I had just about written this project off, and needed a small amp for a Gospel gig this Sunday. Tried it out at our venue, and it fills the room nicely at 3 o'clock volume. It also reacts well to my Tele partscaster. Cool.

http://farm6.staticflickr.com/5345/7050347219_5d5ab6e01e_o.jpg (http://www.flickr.com/photos/charisjapan/7050347219/)
RCS_1868 (http://www.flickr.com/photos/charisjapan/7050347219/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

I'm glad that the problems disappeared with a more correct layout. Thsiis why layouts are soemtimes protected by copyright law. A fellow member here builds a great littel boost pedal. The plans for this effect...and almost all other pedals that are being built today...have been common knowledge for decades. What is important is not particularly the schematic but the lalyout...and he has had to protect his copyrighted PCB from folks who have 'reverse-engineered' the board.
When you changed the layout, you eliminated some...who knows how many....points where unwanted 'signals' were being induced by improper relationship of the wiring. Wtih a more proper layout, these problems disappeared. Wires are now not in close proxiimity in a certain arrangement that would induce unwanted currents. Kudos for going to the trouble of reworking things.

Vibrato/volume....most of us turn the vibrato off if we are not going to use it. I have never incurred the situation that you describe. IT may or may not be 'normal'....I jsut never have 'been there, done that'. Have you worked up a switch to turn it Off? If so, what happens when you do that? That Vib circuit is connected to the speaker out lead through the cathode bypass on pin 8, V1....and there is a relationship there that can only be avoided by turning the circuit 'off' with a switch.

Voltages....the on ly thing that I see that is 'odd' would be the screen grid in the 6V6....it should be closer to the plate votlage. Everything else looks spot on, doesnt' it?

Wally,

Thanks for the reply and kudos! I gotta admit, it feels good to get my first amp build running.:grin:

I did decide to put a switch in where the Vibro RCA connector is. Actually, the Vibro (tremolo) is engaged by default, and shorting to ground the wire from turret 20 on the board. Maybe later I will try to 'interrupt' pin 8 on V1 with a switch, but I will be using the amp for a gig on Sunday, and didn't want to mess anything up, now that I got it going! :razz:

Thanks again!

http://farm8.staticflickr.com/7227/6884877194_bacf260a25_o.jpg (http://www.flickr.com/photos/charisjapan/6884877194/)
Triode AA764 Vibro Champ 40-18027 120V Numbered (http://www.flickr.com/photos/charisjapan/6884877194/) by charisjapan (http://www.flickr.com/people/charisjapan/), on Flickr

YaY, I was so out of ideas on the other board and felt really bad you did not have a working amp yet. I would really like to know what the issue was, to put with my collection of odd problems, but having a working amp and not knowing is still way better then a non working amp and buckets of information. Have a great gig tomorrow.

YaY, I was so out of ideas on the other board and felt really bad you did not have a working amp yet. I would really like to know what the issue was, to put with my collection of odd problems, but having a working amp and not knowing is still way better then a non working amp and buckets of information. Have a great gig tomorrow.

Thanks for the YaY, celeste. The gig was fun, though I was pretty nervous. I didn't freeze up, so it was great!

Indeed, working amp is a LOT better than a miserable failure of an amp build! :cry:

And it is working fine. I am really loving the tremolo, so warm and real. I put a switch in the place of the footswitch jack.

As to the volume/intensity thing, it's my first 'odd problem' and challenging me. The only thing I can see in the layout is that both pots are conneceted to V1 AX7 at pins 7 and 8, but have no clue what that means. (but i'm not going to lose any sleep over it, and it's late in Japan, so...

Be well!

I can't believe it's only been a little over 2 months since I "finished" my first build! And now I'm closing in on the completion of my second, a 5E3 with a 'real' chassis and cab.

I was already salivating after another build when I looked at my VC yesterday. It's kind of on 'permanent loan' to my church band, and everyone that uses it loves the tube tone and just-right volume sweep for our venue. But it looks bad compared to the 5E3, and I came to the conclusion that I would feel a lot better about really finishing the AA764 than starting another project. So....

I haven't really found a nice chassis for a VC, but Memphis Amps, who made my tweed cab, make custom chassis. I'm asking for a quote, as well as a slightly-downsized 5E3 cab for a 10" speaker. Both transformers are already upgraded, 5-15W for the PT (I'm seeing 342V, a nice number) and a 15W OT. I will probably upgrade the resistors and caps, any suggestions? (nothing too expensive, please!) Also, what do you think of keeping the 40-20-20-20 525V Twist-lock, or going to 3 separate filter caps? What values? I have a perf-board and plenty of turrets, so I'm willing to get a little 'out-of-the-box' for layout, but I want to keep the basic SE circuit. Just food for thought, I was told it would be pretty easy to use a 6L6 power tube...

Please, help me 'honorably' finish this amp! :grin:

I got my VC clone chassis from here.http://store.marshamps.com/product_info.php?cPath=24&products_id=278. I guess you can get it from where you are located.

I used an empty 25 Watt Frontman cab, it fit perfectly. Just had to drill new holes for the chassis straps. I went with a ten inch speaker since the cab's baffle was already for a 10.. I also used the triode kit.

Just a thought on the intensity pot issue.

That pot is in parallel with the bias resistor (1.5k) of the 2nd triode of the pre-amp. If the pot were defective it could be shorting the cathode to ground.

Try reading the voltage from pin 8 to ground with the pot turned up all the way, and then down all the way. If you notice any significant difference between the two readings then this is the source of your problem.

I got my VC clone chassis from here.http://store.marshamps.com/product_info.php?cPath=24&products_id=278. I guess you can get it from where you are located.

I used an empty 25 Watt Frontman cab, it fit perfectly. Just had to drill new holes for the chassis straps. I went with a ten inch speaker since the cab's baffle was already for a 10.. I also used the triode kit.

Thanks, Telex!

I do remember looking into Marsh Amps, but $85 plus about $50~60 shipping was pretty steep. The Frontman 25 is hard to find used here, so that is also kind of difficult. I'll just have to see what Memphis Amps quotes for the chassis + cab. :?:

I liked the Triode kit, but was wondering if there was an alternative to the cap can, like Ceriatone? Did you just stick to the Triode layout? Try any mods?

charisjapan

Thanks, Telex!

I do remember looking into Marsh Amps, but $85 plus about $50~60 shipping was pretty steep. The Frontman 25 is hard to find used here, so that is also kind of difficult. I'll just have to see what Memphis Amps quotes for the chassis + cab. :?:

I liked the Triode kit, but was wondering if there was an alternative to the cap can, like Ceriatone? Did you just stick to the Triode layout? Try any mods?

charisjapan

I just did the Triode layout with a few adjustments since I used a vintage type chassis and hardwired the 3 prong plug.
If I was using a chassis that didn't already have a hole for the cap can, I'd just use 3 individual filter caps and put them on the board like a Tweed Champ.

If I was using a chassis that didn't already have a hole for the cap can, I'd just use 3 individual filter caps and put them on the board like a Tweed Champ.

Since I do have a choice, what are my options? Anyone have experience with VC filter cap mods?

Presently I am using the 20-20-20 525V of the cap can. Ceriatone is using separate 33uF-33uF-22uF 450V caps. Fender original is 20-20-20 450V. I'll be seeing about 340V at the PT.

Thanks.

The SE amp I built really benefited from an increase in capacitance on the pentode screen. It brought the hum down while the added capacitance on the plate had much less effect. Since you have a tube rectifier you do not want to go too big on the first stage but with a resistor between the plate and screen capacitors the rectifier tube will not notice an increase at the screen. I would go as big as safe for the rectifier on the first stage and as big as physically possible and economically feasible on the second.

I can't believe it's only been a little over 2 months since I "finished" my first build! And now I'm closing in on the completion of my second, a 5E3 with a 'real' chassis and cab.

So you have the disease...

Since I do have a choice, what are my options? Anyone have experience with VC filter cap mods?

Presently I am using the 20-20-20 525V of the cap can. Ceriatone is using separate 33uF-33uF-22uF 450V caps. Fender original is 20-20-20 450V. I'll be seeing about 340V at the PT.

Thanks.

Separate filter caps are better for eliminating grounding hum. The ground return points in cap cans are all connected - much harder to get rid of AC microwobble in the ground return with cans

Just a thought on the intensity pot issue.

That pot is in parallel with the bias resistor (1.5k) of the 2nd triode of the pre-amp. If the pot were defective it could be shorting the cathode to ground.

Try reading the voltage from pin 8 to ground with the pot turned up all the way, and then down all the way. If you notice any significant difference between the two readings then this is the source of your problem.

Keyser Soze,

Yeah, I keep coming back to that, too. So far, I just don't use it because of the weirdness. :sad: But if I'm going to spend some $ to fix her up, I might as well do it right! I found a local source for CTS 3M reverse-A, but can only find a 50K reverse-A for the intensity. I will test as you said, but do you think the 50K will work? Before I tear it down for a rebuild, I want to get all my parts and mod parts together, rather than getting hung up on one little part. (which will probably happen anyway :wink: )

The SE amp I built really benefited from an increase in capacitance on the pentode screen. It brought the hum down while the added capacitance on the plate had much less effect. Since you have a tube rectifier you do not want to go too big on the first stage but with a resistor between the plate and screen capacitors the rectifier tube will not notice an increase at the screen. I would go as big as safe for the rectifier on the first stage and as big as physically possible and economically feasible on the second.

So you think the Ceriatone 33-33-22 will work?

As usual, supplies are limited here. If I go to a 33uF 450V, my choice is Ruby Gold. 22uF 500V is F&T or IC, and the only (and expensive!) option for 20uF 500V or 600V is the Sprague Atom. I really don't have a brand loyalty thing, and suppose any of these will 'do the job.' Thoughts? :idea:

charisjapan

Nice work! What a difference before and after you re-wired it up. Nice job cleaning it all up and saving the amp.

So you have the disease....

Yeah, I guess a second build confirms it. :sad:

What happens to you on the third build? :shock:

I'm leaning toward separate caps, but I have to admit that it's partly because it looks more cool. :cool:

So... 20-20-20 or 33-33-22, or something else?

I take it you've read Merlin Blencowe's article on Grounding? http://valvewizard2.webs.com/Grounding.pdf

I take it you've read Merlin Blencowe's article on Grounding? http://valvewizard2.webs.com/Grounding.pdf

Have now!

I guess that settles the matter... separate filter caps!

Thanks, tubeswell!

Any advice on values? (I feel compelled to keep asking:neutral:)

20uF at each node is fine.

Don't go above 40 for the first/reservoir cap with a 5Y3G rectifier. (In fact its preferable to keep the reservoir at 20uF for longevity of the 5Y3G, but 40uF will keep the bottom end tighter and most 5Y3G should handle it - although it exceeds the reservoir capacitance rating).

However, the best way of getting rid of hum from ripple current (if that is your concern) in a SE amp, is to use a whole-of-supply CLC filter between the rectifier and the OT/output tube-plate supply node. In the case of this type of amp, you'd use another 20uF cap and a HT choke, which in this type of amp (with a 6V6 output tube) can be a 3-10H, 40mA-rated choke - one of these http://store.triodestore.com/22707.html would work fine. (If you're planning to use a 6L6 output tube, then you'd want a minimum 100mA rated choke)

Keyser Soze,

Yeah, I keep coming back to that, too. So far, I just don't use it because of the weirdness. :sad: But if I'm going to spend some $ to fix her up, I might as well do it right! I found a local source for CTS 3M reverse-A, but can only find a 50K reverse-A for the intensity. I will test as you said, but do you think the 50K will work? Before I tear it down for a rebuild, I want to get all my parts and mod parts together, rather than getting hung up on one little part. (which will probably happen anyway :wink: )

Sure a 50K RA will work, you may just find that a portion of the sweep is not very useful, or maybe not. That pot operates as a voltage divider, shunting the output signal from the cathode follower to ground. What you may find is that once the resistance value rises much above 25k there is no appreciable change in response (or you may find you've created a knob with better adjustment range...)

Some people prefer linear pots in trem circuits, functionally they work the same, but if you like the reponse of an audio taper you can roughly duplicate one by using a linear pot and an equivalent fixed resistor wired from one leg to the wiper (depending on the lug chosen you get pseudo audio taper or pseudo reverse audio taper.

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

The only potential (heh) downside of this approach is that the added paths of resistance can lead to more resistor noise (hiss) but since the trem circuit is not acutally carrying audio signal this is not a concern.

20uF at each node is fine.

Don't go above 40 for the first/reservoir cap with a 5Y3G rectifier. (In fact its preferable to keep the reservoir at 20uF for longevity of the 5Y3G, but 40uF will keep the bottom end tighter and most 5Y3G should handle it - although it exceeds the reservoir capacitance rating).

However, the best way of getting rid of hum from ripple current (if that is your concern) in a SE amp, is to use a whole-of-supply CLC filter between the rectifier and the OT/output tube-plate supply node. In the case of this type of amp, you'd use another 20uF cap and a HT choke, which in this type of amp (with a 6V6 output tube) can be a 3-10H, 40mA-rated choke - one of these http://store.triodestore.com/22707.html would work fine. (If you're planning to use a 6L6 output tube, then you'd want a minimum 100mA rated choke)

tubeswell,

So far, I'm not all that worried about hum. In fact, considering the unconventional layout I made with the existing combo chassis (and my inexperience), I'm amazed there isn't more noise! Mostly I want to make it look better, now that I will have my nice tweed up on stage next to it. But while I'm at it, and spending some money for a chassis and cab, I also have the freedom to upgrade here and there without breaking the bank. I really never liked the idea of 4 caps in a can. from what little knowledge I have gained this past year, it doesn't seem right. New caps and resistors might cost $40~50, and I can tidy things up. :grin:

But if I DO start building at that level, i.e. adding another cap and choke, do you think this one will work? It's a Triad Magnetics C-3X, 50mADC, 10 Inductence Henries, 500 ohms. I'm not sure exactly how that compares to the Triode 40mADC, 4 Henries, 150 ohms? Unless I'm getting some more transformers from Triode, shipping will be a lot more for the choke than the choke itself. :sad:

Triad C-3X Choke (http://www.triadmagnetics.com/catalog_template.php?productCategoryId=68&reference=c-3x)

I thank you for taking the time to give me these tips! As to the filter caps, for the sake of simplicity and maybe a bit of perversity :wink: , I think I'll try the 33-33-22 route. Going all 20s will cost over double, and longevity is not that much an issue to me.

All this is kind of academic until I get a quote for the chassis/cab. Also, we have a mini-concert coming up next month, and I can't mess up the VC until after that. I hope to have my 5E3 up-and-running for that, too! :grin:

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

Thanks, Keyser! Great article. That one goes in my files!

The only potential (heh) downside of this approach is ...

Pun appreciated! :lol:

That choke will work, but aT 500R DC resistance, it will drop a bit more supply voltage than a 150R choke

That choke will work, but aT 500R DC resistance, it will drop a bit more supply voltage than a 150R choke

OK, I am beginning to see how that works. I do need to study more on this, but also on a LOT of other things!

Right now they also have in stock the C-8X, 7H 75mADC DCR 240Ω, but the C-14X 150Ω is out-of-stock. Maybe they'll have it by the time I start the re-build.

In other news, check my 5E3 build in a little bit :mrgreen:

It helps to think of a choke as a 'sort of' constant current device.

Capacitors and chokes perform similar functions in the power section of an amp. They filter noise and they support the power delivery to the rest of the circuit by storing, and then delivering energy.

While capacitors do this by storing charge on their plates and proping up the operating voltages, chokes store their energy in the form of a magnetic field and help prop up the current supply. Capacitors rapidly discharge, so if the circuit pulls faster than they can recharge the voltages will drop (that's sag.) A choke stores much more energy, and is more resistant to change so can help minimize this sag in the power supply (stiffening and improving bass response.)

The first consideration when choosing a choke is current handling capability (milliamp rating.) The choke needs to be able to handle the current draw of everything it supports. Look up the current draw for each tube and add them all (this is plate, and screen current, not heater current.) If it can't handle the total draw then it will burn up sooner or later.

The second consideration is the inductance, the higher the inductance the more energy it stores, which both improves filtration and stiffness/bass response.

The last number, it's resistance, is really just a byproduct of the other aspects (determined by the amount of wire used to make it) and as mentioned affects how much the device will cause voltage to drop in the power supply. Ideally lower is better, but in practice the more henries you desire the higher this number will be. On the plus side a choke is a much better noise filter than a resistor (ie. a C-L-C filters more noise than a C-R-C at equivalent resitance value.)

Mostly lurking and trying to learn on this thread. INTeresting. I understand how the increased fitlering at that first stage and the addition of a choke can affect low frequency 'stiffness'. I also think that the 33mfd that Chris is choosing for that first stage is about the max for a 5Y3...spec'd for 30mfd max, right?
My question is what is the effect of using those 20-22mfd caps for filtering for the preamp? I have read that large filters serving the preamp can lead to overpowering lows in the preamp. Any thoughts on that?

Good discussion point Wally.

The BF vibrochamp came with a cap can with 20 at each node. As far as the 'balance' of signal bandwidth goes, that amp sounds alright (to me).

If you have Merlin Blencowe's 2nd book (on Power Supplies) handy, RC smoothing is explained in theory on pages 69-76. In a nutshell, the currents in a typical pre-amp stage are so low that it practically makes no difference whether you use 8uF or 22uF for the pre-amp node. (The 12AX7 in the vibrochamp's pre-amp draws maybe 2 mA tops, and it is a cascaded inverting pair, so when one triode is pulling more, the other triode is pulling less. And we see from the schematic that there is a measured 20V drop across the 10k dropping resistor - which confirms the 2mA total draw). Seeing as how you want pure DC at the filter cap node, lets assume that the desired voltage noise frequency cutoff is 1Hz, so the capacitance at the pre-amp node necessary to achieve this is:

C = 1/(2Pii.R) = 1/(44/7 x 10,000R) = 0.0000159F (or 16uF). (So 20uF would give an even lower rolloff frequency than 1Hz. - in other words, you're even less likely to hear voltage supply noise)

Once upon a time it was hard to find an e-cap bigger than 8uF, so Fender used 8uF. As cap-making got more efficient, he used more capacitance, because it is better at getting pure DC.

In terms of whether filtering of this magnitude makes any difference to the amount of bass otherwise present in the signal path in this amp, I doubt anyone would notice.

... I have read that large filters serving the preamp can lead to overpowering lows in the preamp. Any thoughts on that?

I agree that there is something to be said for that position, but what actually happens depends not only on the value of the power caps, but also things like the tube being served, it's operating point, coupling cap values, playing style, and -most importantly- the perceptions of the listener.

What I hear from large caps in the pre-amp often isn't so much more bass, but an increased responsiveness that I describe as more of a bark (sharp) than a woof (rounded.) But once the later stages begin to compress/overdrive much of this nuance is lost.

Personally I prefer small caps (5-10 uf) for the earliest pre-amp stages, but that's truly (and entirely) a matter of opinion.

Guys, I can't believe it myself, but I almost understand what you're talking about! :shock:

Surely, as I start making my parts list I will ask for more guidance... and probably end up getting a few extras, both high and low. I not only want to re-build the Vibro Champ, but want to learn more about what's going on inside there! For pure esthetics (and photogenics!) I will want nice, over-spec resistors. I also want to experience the 'orange-drop-vs-mallory' difference. I know there's probably not that much difference, but 'empirical method' is fun! :grin: I doubt (for now) if I'll want to spend a bundle on NOS or used vintage stuff, except maybe those dominos that Andyfromdenver likes to play with. :wink:

I appreciate all input!

charisjapan

In my view a larger capacitor on the preamp PS will not change the frequency response of the circuit but it will change the time constant of the PS. A smaller capacitor will have the voltage sag a bit quicker than a larger when the upstage power supply capacitors sag. The sag will decrease the voltage out of that stage which will change the amount of drive the downstream stages get. This may effect the dynamic distortion characteristic of an amp. Guess I should mention the amp would have to be Class AB as Class A does not change the current demand enough.

Well, I love the Tweed 5E3 so much that I'm thinking of getting a tweed cab built for the Vibro Champ. Yeah, I know it's a Blackface, but... Let's just say I consider it a prototype single-ended 5W Tremolux, or whatever. :grin:

I am going to get a cab made for a 10" speaker, maybe 1~1-1/2" narrower and a little shorter than a 5E3. I hope to keep about the same proportions. But a Vibro Champ has a few more pots, so I can't make the chassis very much smaller without ditching the chickenheads... NOT going to happen!

So here's a drawing I made, and I would like to get your input about the layout. In case you're wondering, I used a OFF/STANDBY/ON switch and added a Tremolo switch instead of the footswitch. I appreciate your help! (again :wink: )

http://farm8.staticflickr.com/7264/7447529680_e014cdb26c_b.jpg (http://www.flickr.com/photos/charisjapan/7447529680/)

charisjapan

http://farm8.staticflickr.com/7264/7447529680_e014cdb26c_b.jpg (http://www.flickr.com/photos/charisjapan/7447529680/)

charisjapan

I'd keep the big tubes sockets further apart from each other, especially when they're hanging 'upside down' in a tweed-style chassis (remembering that the heat will rise). Bigger tubes dissipate a lot of heat. As a RoT its good to have at least 1.5 x to 2 x the diameter of the tube spacing between big tubes - but the further apart the better to keep them cool. You appear to have a bit more real-estate in your design to accommodate this. JM2CW

PS - Also you may find you don't have enough space between the lamp holder and the adjacent pot and switch/fuse. (Remember that the classic tweed style bayonet lamp holder hole is 11/16", but the actual lamp holder is bigger than this) When you taken account of the fact that there are wires etc to be routed everywhere, you may find things a bit cramped. Just sayin'.

I'd keep the big tubes sockets further apart from each other, especially when they're hanging 'upside down' in a tweed-style chassis (remembering that the heat will rise). Bigger tubes dissipate a lot of heat. As a RoT its good to have at least 1.5 x to 2 x the diameter of the tube spacing between big tubes - but the further apart the better to keep them cool. You appear to have a bit more real-estate in your design to accommodate this. JM2CW

PS - Also you may find you don't have enough space between the lamp holder and the adjacent pot and switch/fuse. (Remember that the classic tweed style bayonet lamp holder hole is 11/16", but the actual lamp holder is bigger than this) When you taken account of the fact that there are wires etc to be routed everywhere, you may find things a bit cramped. Just sayin'.

Tubeswell,

Thanks for the advice! Good point, I moved the octals to be 3" apart and the preamps 2" apart. Re the top panel, yeah, it's gonna be tight! :sad: I wanted to narrow it down from the 5E3, but only shaved 1/2". I figure my cab maker will be able to trim the width of the cab 1-1/2" and still get this chassis in there, and still keep the proportions I'm looking for.

I measured the controls, and came up with a installation 'flow chart.' Lamp first, then fuse, then switches, then jacks, finally pots. If I use star-washers, I can tighten everything down from the outside, except the lamp and fuse. The spacing allows the chickenheads to do what they do.

The Standby/On switch is a Carling DPTTP (Double Pole Triple Throw Progressive). I could go with 16mm pots, but that won't make the chickenheads any smaller. The turret board I will be making from a perforated plate, and have already made a layout using 3 separate filter caps. I'll post that for ideas a bit later.

Thanks, and hope others will give me some tips!

http://farm9.staticflickr.com/8153/7451420148_6d79014a94_b.jpg (http://www.flickr.com/photos/charisjapan/7451420148/)

You need a hole for your power cord and strain relief. Drawing looks great, BTW. Cool project.

Look at who's all grown up and rolling his own amps now. Just thinking back when someone was just getting their feet wet.

You need a hole for your power cord and strain relief. Drawing looks great, BTW. Cool project.

Oops!

Yeah, and for OT mounting bolts and wires :oops: Come to think of it, I have a multi-Ohm OT, so a mini-toggle near the speaker jacks.

After wrestling with this for a couple days, I can see why folks don't go around making custom chassis every day! That, and Tweed to Blackface was a major layout change...

Look at who's all grown up and rolling his own amps now. Just thinking back when someone was just getting their feet wet.

Hehe! I'll only be 'growed up' when I get this thing to work! :wink:

(and if I can afford it... I haven't gotten the estimate yet :shock: )

But isn't it fun trying to figure it all out? That is what keeps me at it, could have bought some nice amps with the amount I spent on parts. Speaking of parts, there are a couple of different sizes of chicken head knobs. I picked up some larger ones, just got some smaller ones that are 32mm, and I see there are some 20mm knobs.

http://www.gravitech.us/redchhekn141.html


Oh, and the getting it to work thing, go through that also.

But isn't it fun trying to figure it all out? That is what keeps me at it, could have bought some nice amps with the amount I spent on parts. Speaking of parts, there are a couple of different sizes of chicken head knobs. I picked up some larger ones, just got some smaller ones that are 32mm, and I see there are some 20mm knobs.

http://www.gravitech.us/redchhekn141.html


Oh, and the getting it to work thing, go through that also.

Oh, yeah, DIY is one thing, to save money or gain experience or self-satisfaction or whatever... But DIMW (Do It My Way), and have it work is another thing altogether. :wink: And yes, it's true, if you calculate parts, tools, mistakes, and time spent, 'boo-teek' amps don't seem that expensive anymore. :rolleyes:

Those 20mm chicken heads are still 32mm total. :neutral: Either way, much smaller and the 24mm pots become the problem. What I'd like to find is an outrageously large chicken head for my Champ 600. lol! If it' gonna be just one knob, it should be HUGE!! :grin:

But isn't it fun trying to figure it all out? That is what keeps me at it, could have bought some nice amps with the amount I spent on parts. Speaking of parts, there are a couple of different sizes of chicken head knobs. I picked up some larger ones, just got some smaller ones that are 32mm, and I see there are some 20mm knobs.

http://www.gravitech.us/redchhekn141.html


Oh, and the getting it to work thing, go through that also.

Heck you've got big coins over here!!

I just noticed that you intend to have a trem switch on the control panel. To save some real estate there, you could dump that switch and instead use a combined pot/switch on the depth pot, or just use a footswitch into a jack on the underside of the chassis (which is more versatile for live playing anyhow)

I just noticed that you intend to have a trem switch on the control panel. To save some real estate there, you could dump that switch and instead use a combined pot/switch on the depth pot, or just use a footswitch into a jack on the underside of the chassis (which is more versatile for live playing anyhow)

Thought about that...

But I could only find a 1MA pot here, and using the volume pot for switch would not be 'intuitive.' I found a 25KA push/pull, but it's not Reverse Audio, and might be a bear to adjust sweep. :confused:

If I decide to go a footswitch, I might consider a double switch, and make the second a 'boost' switch a la Ceriatone's Champ Ultra. Seems it's just a tone stack cutout, and to some degree reverts the amp to a 5F1 w/tremolo. Anyone have experience with that circuit?

Ceriatone Champ Ultra Layout (http://www.ceriatone.com/images/layoutPic/fenderLayout/Champ-Ultra-Layout.jpg)

Well there's no real reason the intensity pot has to be antilog taper (except that it changes when the trem kicks in on the pot rotation - which you might or might not mind too much about).

However, if you're prepared to experiment a little, you could use a normal audio pot but put an antilog taper resistor on it. Hoffman has 50k Audio pots with SPST switches for US$3.75.

http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=PotsKnobs&ORDER_ID=!ORDERID!

You could use that in place of the 25k and you could put a 22k antilog tapering resistor on it (between the pot input and the pot wiper).

http://www.geofex.com/article_folders/potsecrets/revlog.gif

Then you will have a log/antilog taper which should help a bit. (However no guarantees given)


Or - you could rewire the intensity control differently so that it works with an audio taper pot (e.g. use a conventional 100k load resistor on the CF stage and AC-couple it with say a .1uF coupling cap to the input lug of a 50k pot (which could an audio pot with a switch), and hook the pot wiper to the pre-amp cathode (pot ground lug goes to ground). If it is too strong just add a suitable resistor between the coupling cap and the pot's input lug to knock the voltage down a bit more. There you go

Well... There you go

:neutral: ... :confused: ... :shock: ... :cool:

I (kinda) got it. And maybe a little headache. :wink:

I think for now I'll just reclaim a little real estate (1/2"?) by using a footswitch for the trem and maybe the tonestack bypass 'boost.' But I've heard there's a big gain jump when you go from BF to Tweed. Hmmm...

Ideas? :idea::?:

The tweed champ doesn't have a tone stack to load down the V1 stage, so its the simplest and most gainy of those amps. Mind you the 5F2A (one-knob) 'tonestack' is pretty simple and effective for what it is, and has the next least-amount of load, and it is also pretty gainy.

You could lift the BF tonestack in the vibrochamp by putting a SPST switch between the 18k resistor and the ground for a 'rawer' sound.

2" knob

http://www.ebay.ca/itm/Large-2-Black-Chicken-Head-Pointer-Knob-Found-Older-Test-Equipment-2-Lot-/290696786873?pt=Vintage_Electronics_R2&hash=item43aee0f3b9

40mm

http://www.ebay.ca/itm/Large-Chicken-Head-Pointer-Knob-6mm-0-25-Inch-Shafts-Volume-Tuning-Knob-/120824692617?pt=UK_Mobile_Phones_Communication_Rad io_Parts_Accessories&hash=item1c21b67f89

I picked up some 40mm (1.6") knobs a while back.

[QUOTE=printer2;4260451]Large 2" Black Chicken Head Pointer Knob[QUOTE]

Printer,

'Dem ain't chicken heads, dey's Pterodactyl Heads!

So I bought a pair! :grin: (one for my Champ 600 RI, another for... ?)

http://farm9.staticflickr.com/8003/7457984096_9baac9de22_z.jpg (http://www.flickr.com/photos/charisjapan/7457984096/)

The tweed champ doesn't have a tone stack to load down the V1 stage, so its the simplest and most gainy of those amps. Mind you the 5F2A (one-knob) 'tonestack' is pretty simple and effective for what it is, and has the next least-amount of load, and it is also pretty gainy.

You could lift the BF tonestack in the vibrochamp by putting a SPST switch between the 18k resistor and the ground for a 'rawer' sound.

That BF >> Tweed is precisely what I want, but I've read that the jump in gain is rather sudden. Is there any way to lessen the surge without losing that full tweed 'brattiness?' I don't want to add any more switches or knobs on the control plate, so the SPST switch will have to be on a pedal with the SPST for the trem. The amount of boost might be just right, who knows? :confused:

You might want to put in a couple of resistors for the mid control, one the 6.8k that normally is in a BF Champ, and a 20k in series below it. You could have the switch on your pedal closed which would short out the 20k resistor giving you the standard BF sound. Then when you open the switch the resistor would be in series and you would get more of a flat response rather than the big scoop.

You still get about 10dB of loss though, if you have not already done so, try the tone stack calculator. Hours of fun.

http://www.duncanamps.com/tsc/

...try the tone stack calculator. Hours of fun.

Printer,

Just what I need, hours of "fun." :neutral:

For now, I think I'll just have to remember (and remind others that use the amp) to knock the guitar volume down a notch when engaging 'Tweed Madness.' lol!

But yeah, that's a thought for future tweaks. Another that came to mind was a separate volume knob. In order not to use any real estate, maybe a dual-pot/split-knob? Hmmm... split chicken head? :!:

My latest layout returns the trem-switch to a foot-switch. This gets the chassis back down to 13-1/2" which should make a nice-sized cabinet with correct proportion. If I use the tone-stack cutout switch, I won't feel bad about the tweed motif! :wink:

Comments?

http://farm9.staticflickr.com/8149/7458654872_9aced4b96f_b.jpg (http://www.flickr.com/photos/charisjapan/7458654872/)

How about puting the fuse on the bottom with the tubes. I am doing that on mine. How often do you change a fuse?

How about puting the fuse on the bottom with the tubes. I am doing that on mine. How often do you change a fuse?

I hope to never change the fuse! Did these things blow fuses that often 50 years ago? But since I'm going tweed, I thought it would look a little lonely up there without it. :wink:

Now I have to think what kind of faceplate and the lettering. I suppose the standard is chrome with white lettering...

That BF >> Tweed is precisely what I want, but I've read that the jump in gain is rather sudden. Is there any way to lessen the surge without losing that full tweed 'brattiness?' I don't want to add any more switches or knobs on the control plate, so the SPST switch will have to be on a pedal with the SPST for the trem. The amount of boost might be just right, who knows? :confused:


Difficult to do nicely without a better taper on the volume pot. Most off-the-shelf pots these days have '2-line' tapers with an abrupt knee in the middle (instead of a nice logarithmic curve), where the rate of change of resistance changes abruptly at one point as you increase the pot rotation. The problem is exacerbated on champs because there is no parallel tone stack to add to the load and reduce the brash effect of the '2-line' breakover/knee point in the pot taper. You could maybe hunt around for a quality old NOS 1MA pot.

Guys, I can't believe it myself, but I almost understand what you're talking about! :shock:

Along the lines of my PM to you just now (but for the benefit of others who may want to understand) regarding tremolo:

Merlin Blencowe's page here http://www.freewebs.com/valvewizard1/trem1.html may help you to understand the basics of trem circuits.

Your basic LFO (low frequency oscillator) stage is already an 'inverting' stage (meaning that the signal at the plate is the opposite phase to the signal at the grid) - we say that the signal at the plate is 180 degrees out of phase with the signal at the grid.

A R/C (resistor/capacitor) feedback network connects the plate to the grid, and this puts the signal almost 360 degrees out of phase, which is fed back to the grid and causes the gain of the stage to self-oscillate at a rate which is determined by the combination of resistance and capacitance values in the R/C feedback network. So the voltage output of the stage goes up and down and up and down and so on.

This changing voltage is tapped off the plate, and is either buffered by a simple cathode follower stage, or fed directly to the default bias mechanism of the stage in the signal path that you are wanting to be affected by the tremolo effect. (If the stage you're wanting to affect is cathode-biased, the trem output is usually attached to the cathode. If its fixed-bias, the trem output is usually attached to the grid). So the trem affects the stage in the signal path by changing that stage's bias (voltage) point. The colder the bias (i.e.: the higher negative bias voltage) the more the signal tube is in 'cutoff', where the output volume is decreased. That is how the trem affects the signal.

A simple voltage divider between the output of the oscillator and the stage that you're wanting to oscillate, controls the intensity of the changes in voltage from the LFO. Varying one or more of the resistors in the LFO's R/C feedback network changes the rate of oscillation.

Difficult to do nicely without a better taper on the volume pot. Most off-the-shelf pots these days have '2-line' tapers with an abrupt knee in the middle (instead of a nice logarithmic curve), where the rate of change of resistance changes abruptly at one point as you increase the pot rotation. The problem is exacerbated on champs because there is no parallel tone stack to add to the load and reduce the brash effect of the '2-line' breakover/knee point in the pot taper. You could maybe hunt around for a quality old NOS 1MA pot.

I DO notice that weird sweep in audio pots. It's certainly not smooth logarithmic!

My local supplier carries a PEC MILspec K-series 1MA pot. Their blurb says "Hot Mold Carbon" element. They cost about 3X the CTS pots, but do they have a smoother sweep? They look like they're indestructble. :shock:

Along the lines of my PM to you just now (but for the benefit of others who may want to understand) regarding tremolo:

Merlin Blencowe's page here http://www.freewebs.com/valvewizard1/trem1.html may help you to understand the basics of trem circuits.

Your basic LFO (low frequency oscillator) stage is already an 'inverting' stage (meaning that the signal at the plate is the opposite phase to the signal at the grid) - we say that the signal at the plate is 180 degrees out of phase with the signal at the grid.

A R/C (resistor/capacitor) feedback network connects the plate to the grid, and this puts the signal almost 360 degrees out of phase, which is fed back to the grid and causes the gain of the stage to self-oscillate at a rate which is determined by the combination of resistance and capacitance values in the R/C feedback network. So the voltage output of the stage goes up and down and up and down and so on.

This changing voltage is tapped off the plate, and is either buffered by a simple cathode follower stage, or fed directly to the default bias mechanism of the stage in the signal path that you are wanting to be affected by the tremolo effect. (If the stage you're wanting to affect is cathode-biased, the trem output is usually attached to the cathode. If its fixed-bias, the trem output is usually attached to the grid). So the trem affects the stage in the signal path by changing that stage's bias (voltage) point. The colder the bias (i.e.: the higher negative bias voltage) the more the signal tube is in 'cutoff', where the output volume is decreased. That is how the trem affects the signal.

A simple voltage divider between the output of the oscillator and the stage that you're wanting to oscillate, controls the intensity of the changes in voltage from the LFO. Varying one or more of the resistors in the LFO's R/C feedback network changes the rate of oscillation.

While I have to admit that a lot of that zoomed over my head, I have been chewing on this subject for the past few months, and there's a glimmer
of understanding creeping in... It helped that I spent some time earlier today playing with the VC trem controls. Your explanation 'clicked' with what I was hearing.

I've read some of Merlin Blencowe's stuff at valvewizard, but right now they've used up their allotted bandwidth, so I'll have to get back to that article after the first of the month.

Thanks always for the informative posts, tubeswell!

Btw, I sent in the drawing to get a quote on the chassis and cab... Now I have to save those shekels for those. But I think it will be cool to have a tweed 5F1/AA764 convertible! :grin:

Well, got the estimate, and it's even less than I was fretting about. Just waiting for the credit card billing cycle to 're-fresh.' :roll:

Seems the faceplate is black aluminum with engraving, so I get to choose a name. "Vibro Champ" doesn't seem quite right on a tweed, and "Tremolo Champ" is more correct, but not very catchy... any ideas? :idea:

How about puting the fuse on the bottom with the tubes. I am doing that on mine. How often do you change a fuse?

Printer,

Well, in the end I am doing exactly what you advised. I wanted the 'continuity' with the standard tweed image, but that was gone already with 5 pots on top! :neutral:

So Bruce suggested to put the fuse below, and make the faceplate less cluttered, so I sent in the final design. Now he's gonna 'fix' my noob mistakes and balance things out, and work on the engraving. His chassis is aluminum, with a separate aluminum faceplate. Because polished aluminum looks terrible after a few years, I asked him to look into gold enamel or anodized, with engraved lettering.

I should get a layout from him after things settle down from the Fourth celebrations. :grin: That's one of the things I miss from the States. Japan has a completely different summer mood. Its more frantic, because school vacation is only 5 weeks, and workers usually only get one week of national holidays in August, which means 120 million folks take their vacations at the same time! That's when I stay home. :shock:

So now I just wait for cab/chassis to arrive.... waiting .... ....

charisjapan

Merlin Blencowe's page here http://www.freewebs.com/valvewizard1/trem1.html may help you to understand the basics of trem circuits.

:cry: This page is still unavailable. I was able to get the text from Google's cache, but not the diagrams, as freeweb doesn't allow a cache. But I did study the text, and it was enlightening. Actually, you already said most of it! :grin:

Well, maybe not final as in what Bruce will make, but as far as my drafting abilities go. I forgot to post the pic!

Hope ya'll (you'ns, you'se?) in the USofA are enjoying the Fourth holiday! Weather-permitting, a good number of you will be at a park picnic eating chicken, ribs, hot dogs and hamburgers and guzzling whatever carbonated beverage you prefer 'til you are ready to burst. "TUMS" and sunburn lotion blessings to all! :grin: (Man, I miss it!!)

http://farm9.staticflickr.com/8288/7492204594_7c3554b84f_b.jpg (http://www.flickr.com/photos/charisjapan/7492204594/)

:cry: This page is still unavailable. I was able to get the text from Google's cache, but not the diagrams, as freeweb doesn't allow a cache. But I did study the text, and it was enlightening. Actually, you already said most of it! :grin:

If you PM me with your email addy, I'll flick you a .pdf version which includes the diagrams

Hey all,

Well, it's been a while since I started thinking about re-building my first amp build. I think I said all this before, but it's been almost 6 weeks since my last post on this thread. I am having a 10" speaker size tweed cab built by Memphis Amps, and Bruce tells me it's ready to send! He's making me a custom chassis as well. It will be about the same size as a 5F2A cab, but have all the BF Vibro Champ controls. I'm thinking about a NFB bypass and a tonestack cutout to get me into tweed circuit territory at will. I just finished the layout for the turret board I am making from pre-punched board, so thought I might try an on-board solid state rectifier (just for fun).

Please take a peek and tell me if I made any errors. I will post a pic of the components I have gathered, after I see if they will really fit like I'm showing them here. :wink:

Cheers!

http://farm8.staticflickr.com/7118/7780986874_7209957b2b_b.jpg (http://www.flickr.com/photos/charisjapan/7780986874/)