Ampeg V-4/VT22 Build

[pompeiisneaks]

I'm starting the prep work on an Ampeg V4/VT22 build with a few modifications:

1. I'm only doing one channel, there are two channels but they're identical save for each having their own sensitivity switch, but i figure that's something I can just tweak to liking on the one channel. 
2. I'm removing the reverb, as I've got a reverb pedal, and I'm trying to reduce the overall complexity of the build
3. I'm replacing the 6K11 compactron tube with two tubes, a second 12DW7 since that tube has the u 100/22 like the two of the compactron, and I'll use a 12AX7 half for the other part since they're pretty pricey and aren't being made anymore. (I may mod some part of the input to use the other half as additional gain, but only after the amp is built... not sure yet, because I guess I'd want to have the turrets setup first?)
4. Going to set this up for 6550's instead of the 7027A for the same reason as the compactron above, scarcity. 

My first question is about the reverb.  I'm attaching a photo, and removing it seems to me to mean I can remove the mixing resistors that were setup to mix reverb return in with the main channel.   Does this image look right?  I've circled the 180k and 270k resistors I think I should just remove now that I'm not getting a reverb return.  Does that look right?

Any other comments about it in any way are welcome.  (Including dissuading me from the planned actions above :D ) I'm working on the layout now. 

The schematic is here in hoffman's library: http://el34world.com/charts/Schematics/files/ampeg/AmpegVT22_V4_RevA.pdf

and of course my suggested tweak to where the input and reverb mix at the next stage.

~Phil

[pompeiisneaks]

Oh one other modification, I think I'm actually looking at doing the V2 really, with only 2 output tubes instead of 4, I don't need that much output in my mind, 50W is fine :)

[PRR]

> 6550's instead of the 7027A for the same reason

No; because you are not 15 anymore and you don't want "starter tubes" that will fail.

I don't like the idea. The VT40 is very overstressed. 530V on G2 was insane (Ampeg lowered this on a later model). It is not dirt-common so the iron is expensive. Nobody ever really knows how to use the MID control.

I also think much of the tone of these amps is in the speaker.

When I had a blown-up VT-40, I agonized, then installed a Bassman PT for about 400V. Half the power, but a lot less stress.

I'm not saying "no". I'm saying "think".

[sluckey]

If you remove R16 you will need to replace it with a jumper. Removing R17 will totally disconnect the output of the reverb circuit. This is the easiest option.

But, depending on how true you want to keep the original circuit, consider this... Use the original value for R16. Replace R17 with a 420K resistor that connects to ground. If you look closely you will see that R17 connects to a 150K (R104) to ground. 270K plus 150K is 420K. These resistors and R16 make a voltage divider that reduces the signal being passed on to C8. If you simply 'remove' R17, the signal passed to C8 will increase. Is this a big deal? Maybe, maybe not. But I would design the board layout to accommodate this circuit. Then you can easily try both options to know if it's important to you. Just something to think about...

A similar situation exists when eliminating a channel on an AB763 amp. The gain increase is very noticeable if you simply remove the mixing resistors. Some like it, some don't.

[pompeiisneaks]

> 6550's instead of the 7027A for the same reason

No; because you are not 15 anymore and you don't want "starter tubes" that will fail.

Meaning I should just use some 6L6's at lower voltage? (from below comment on 530V as well?)  This means I'll need to adjust the dropping resistors from the power side to the preamp area to ensure I don't drop too low I'd surmise as well?)

I don't like the idea. The VT40 is very overstressed. 530V on G2 was insane (Ampeg lowered this on a later model). It is not dirt-common so the iron is expensive. Nobody ever really knows how to use the MID control.

I also think much of the tone of these amps is in the speaker.

When I had a blown-up VT-40, I agonized, then installed a Bassman PT for about 400V. Half the power, but a lot less stress.

I'm not saying "no". I'm saying "think".

So I think it may be better to do 6L6GC's and say a Bassman PT?  As noted then I'd need to reduce the dropping resistors some and I can go for lower filter caps since this is dual 350's and I could likely get some decen 500V caps for power. 

This does make me wonder one thing I've never really gathered.  How much of an amp's tone comes from the power side vs the preamp?  I hear people say EL34's sound quite different from 6L6's?  IS that just the pentode vs beam tetrode sound?  Am I changing the tonality of the amp heavily by moving to different tubes?  Or does it just reduce overall wattage output?

~Phil

[pompeiisneaks]

If you remove R16 you will need to replace it with a jumper. Removing R17 will totally disconnect the output of the reverb circuit. This is the easiest option.

But, depending on how true you want to keep the original circuit, consider this... Use the original value for R16. Replace R17 with a 420K resistor that connects to ground. If you look closely you will see that R17 connects to a 150K (R104) to ground. 270K plus 150K is 420K. These resistors and R16 make a voltage divider that reduces the signal being passed on to C8. If you simply 'remove' R17, the signal passed to C8 will increase. Is this a big deal? Maybe, maybe not. But I would design the board layout to accommodate this circuit. Then you can easily try both options to know if it's important to you. Just something to think about...

A similar situation exists when eliminating a channel on an AB763 amp. The gain increase is very noticeable if you simply remove the mixing resistors. Some like it, some don't.

that totally makes sense,  I'll definitely keep in a 420k there to ground.  Thanks. 

~Phil

[DummyLoad]

i have a 72-73 V4 that i restored - it had a blown OT and was literally a basket case. got it missing cabinet pieces, a previous tech gooped up and rigged in PS filter botched repair job, see pics in link below, also, the reverb tank needed repair. most of the magic in that amp IS the reverb circuit and IMO leaving it out would be a shame. the tank is an odd impedance but still in production and the tube compliment is also odd but still obtainable NOS.

for power tubes i installed a quad of grove-tubes 6L6GC-GE and they seem to holding up fine so far. you can ask heyboer to wind the PT 50V or so lower, or as PRR states, just use the PT out of a twin reverb: if mine lets go, that's probably what i'll replace it with, that or a hammond 270 series. the iron in the originals is HUGE and 6550's swap in with a minor bias mod without much effort. 

the V4 is one of my favorite amps to play: i play it though a custom cabinet with 1 x 15" and 1 x 12".

https://www.dropbox.com/sh/q7oapfktll8reuy/AABqjTbuqgQBMderNOnyHOzIa?dl=0

--pete

[NewYorker]

Phil:

I feel the need to take a step back and ask - what are you trying to accomplish in this project?

I've been around long enough to remember when the VT-22 first arrived on the scene.  I remember a local guy who had an ES-335 plugged into an early VT-22, which got my attention.  I even played through one once (first generation), and, no, I couldn't figure out the Mid control either.  However, I played a gig where a better player was plugged into the same amp, and ... holy cow!  And another bandmate loved using it with his Fender Rhodes piano.

So, are you prepared to go out to the edge where these amps operated?  Or, play it safe?  Just asking  .

Ed

P.S. I also get the practicalities of not having the original parts available, cost of off-the-wall transformers, etc.

[pompeiisneaks]

i have a 72-73 V4 that i restored - it had a blown OT and was literally a basket case. got it missing cabinet pieces, a previous tech gooped up and rigged in PS filter botched repair job, see pics in link below, also, the reverb tank needed repair. most of the magic in that amp IS the reverb circuit and IMO leaving it out would be a shame. the tank is an odd impedance but still in production and the tube compliment is also odd but still obtainable NOS.

for power tubes i installed a quad of grove-tubes 6L6GC-GE and they seem to holding up fine so far. you can ask heyboer to wind the PT 50V or so lower, or as PRR states, just use the PT out of a twin reverb: if mine lets go, that's probably what i'll replace it with, that or a hammond 270 series. the iron in the originals is HUGE and 6550's swap in with a minor bias mod without much effort. 

the V4 is one of my favorite amps to play: i play it though a custom cabinet with 1 x 15" and 1 x 12".

https://www.dropbox.com/sh/q7oapfktll8reuy/AABqjTbuqgQBMderNOnyHOzIa?dl=0

--pete

Man that was a MESS, electrical tape?  oh my.

Great photo's it looked a TON better there at the end. 

[pompeiisneaks]

Phil:

I feel the need to take a step back and ask - what are you trying to accomplish in this project?

I'm trying to reproduce the main signal chain of the amplifier, preamp and power amp side, tone stack, etc.  I tend to get my effects from the footpedals, I have a great reverb, delay and a few overdrive.  I definitely don't need two channels unless I were to jumper them for more gain, but then again, I'm trying more for the original sound.  I am hesitant to pull the reverb out entirely, it's something I'm still debating.  I may keep it.

I've been around long enough to remember when the VT-22 first arrived on the scene.  I remember a local guy who had an ES-335 plugged into an early VT-22, which got my attention.  I even played through one once (first generation), and, no, I couldn't figure out the Mid control either.  However, I played a gig where a better player was plugged into the same amp, and ... holy cow!  And another bandmate loved using it with his Fender Rhodes piano.

So, are you prepared to go out to the edge where these amps operated?  Or, play it safe?  Just asking  .

Ed

P.S. I also get the practicalities of not having the original parts available, cost of off-the-wall transformers, etc.

I definitely want a great amp, but I don't need to keep it in the original massively high voltage either.  The biggest reason I'm curious about the tonality of the amp, is that one of my favorite quitarists plays through one.  Joshua Homme of Queens of the Stone age.  My last amp was a Vox AC30/4 that I built due to my love of the Edge from U2's sound (that and many other great vox players.  Radiohead are another of my favorite bands and several there use Vox AC30's) 

I started the hobby because I can't afford to go buy the classic amps, but I'm not a fan of the newer crummy circuit board cheap ones.  (I am not against circuit boards, some companies do them very well, but most tend to focus on cheap, not quality)

~Phil

[PRR]

Talking out of school here, but I chatted with a guy asked to "replace Josh, the singer/ guitarist's, vintage Ampeg VT40s (which went wrong all the time and were causing many headaches)."

Which may not deter a hobbyist who is not on the road constantly for contracted concerts.

[pompeiisneaks]

yeah I'm aware, he's moved to using custom amps, I think I heard the same thing and that's why he's moving off of them.  You are correct, as a hobbyist, I'm doing it for fun and to learn, but I'm also open to the idea that this isn't an amp worth doing, and I have other ideas on the horizon, or is there even a different ampeg worth building? 

~Phil

[jjasilli]

for power tubes i installed a quad of grove-tubes 6L6GC-GE and they seem to holding up fine so far.
Ditto.  I have an early '70's V2 I bought used.  It came with a quad of Groove tube 6L6's.  They worked fine.  I didn't like their tone in this amp and replaced them (with a pair of) 7027a's.  However the Groove Tubes do sound fine to me in other amps. YMMV.

[NewYorker]

Sigh!!!

Bear in mind that I came of age, relative to guitars and amps, around 1969-1973.  As I recall, the guitar/amp landscape was more diverse at that point in time.  In the amp space, we hadn't quite yet arrived at the Fender/Marshall/Vox paradigms.  Heck, there was a pretty good local band that played through four Martin SS-140 solid state amps and sounded good doing so.  And Kustom and Acoustic and others were out there.

I guess the fact that there is no "A" in the FMV (Fender/Marshall/Vox) acronym says something.

My earlier point was that, if you're trying to get that original VT-22 vibe, be prepared to jump through some hoops and to bear the subsequent burdens.  On the other hand, there are some other, more well-trod paths that you can follow.

Good luck,

Ed

[pompeiisneaks]

Sigh!!!

Bear in mind that I came of age, relative to guitars and amps, around 1969-1973.  As I recall, the guitar/amp landscape was more diverse at that point in time.  In the amp space, we hadn't quite yet arrived at the Fender/Marshall/Vox paradigms.  Heck, there was a pretty good local band that played through four Martin SS-140 solid state amps and sounded good doing so.  And Kustom and Acoustic and others were out there.

I guess the fact that there is no "A" in the FMV (Fender/Marshall/Vox) acronym says something.

My earlier point was that, if you're trying to get that original VT-22 vibe, be prepared to jump through some hoops and to bear the subsequent burdens.  On the other hand, there are some other, more well-trod paths that you can follow.

Good luck,

Ed

Oh I've been debating what I'm building next for a while, and the complexity of that beast would be worth it if I knew it was going to put out a great thing, but I've also heard and read things that make that specific amp a questionable effort.  I still may, I may not, I've got plenty of time and options. (or so I hope).  I may go for something simple like a Tweed Deluxe or some such too.  Not sure.  I also need to finish up my little bedroom amp project I put on hold to build the last Vox :)

~Phil

[DummyLoad]

for power tubes i installed a quad of grove-tubes 6L6GC-GE and they seem to holding up fine so far.
Ditto.  I have an early '70's V2 I bought used.  It came with a quad of Groove tube 6L6's.  They worked fine.  I didn't like their tone in this amp and replaced them (with a pair of) 7027a's.  However the Groove Tubes do sound fine to me in other amps. YMMV.

a quad of svetlana 6L6GC are on the "to buy" list.


--pete

[HommeMarrBuckley]

Talking out of school here, but I chatted with a guy asked to "replace Josh, the singer/ guitarist's, vintage Ampeg VT40s (which went wrong all the time and were causing many headaches)."

Which may not deter a hobbyist who is not on the road constantly for contracted concerts.

been off the forum for awhile but glad to return to read this.  Nize.  (Sorry Phil if off topic)
A little too old to follow what little heroes I have but was curious why he started using different amps (checkmate, eh185, greetdtone) didn't know if he was just tired of vt-s or what (have read he has used beat gorilla practice amps for recordings as well)  But again, I always felt you use what you use but make it yours.  Wonder the stones impression of using them but that was probably short-lived, as well, outside the ad campaign.  never knew they were prone to problems.

[PRR]

> never knew they were prone to problems.

VT Ampegs are reasonably well built, but complicated, thus cost-challenged.

IMHO the original 7027 tubes are worked FAR too hard to live.

As suggested by the dealer-option 6550 for heavy duty use.

However most were sold to garage-rockers because they were the most bang and LOUD for the buck. So hard life, neglect, abandonment have taken their toll. If someone does want to fix one, it is a real nightmare. I was sad because a failed 7027 burned-up the power transformer. However that's maybe the EASIEST part to replace, if you can source another. Tougher before the Internet, today it is just money. As I always thought the beast was just too darn LOUD for a jazz school, I re-ironed to a lower voltage and lived happy ever after. (It lasted until I left and moved away.)

[DummyLoad]

they are a nightmare to work on if you have to replace a pot. the rest isn't too bad. the 6550 mod is probably the path i'll walk with it as really don't want to spend $$ on a replacement PT. replacing the OT was painful enough on the wallet...


--pete

[pompeiisneaks]

I thought that there's no need to mod at all for pretty much any of the common tubes like 6550, 6l6 etc, they intentionally setup the output stage to make it just work?  (Something I read somewhere that escapes me now).

~Phil

[DummyLoad]

i would mod the bias supply for 6550. there's technically no mod needed for 6550, however, i like the idea of being able to run them cooler if so desired.


--pete

[DummyLoad]

http://www.ampegv4.com/7027.php


last paragraph - author states that R50 needs to be changed to 82K - it's a 56K in stock 7027 trim...


--pete

[pompeiisneaks]

ahh so I'd read the page linked in there: http://www.triodeel.com/7027.htm
and it didn't mention needing anything except for EL34's needing the pin 1 to 8 tied and adjusting the screen to at least 1k. Interesting though, thanks for taht, I'd been on this page before (ampegv4.com) but never seen this particular page! 

~Phil

[DummyLoad]

ahh so I'd read the page linked in there: http://www.triodeel.com/7027.htm
and it didn't mention needing anything except for EL34's needing the pin 1 to 8 tied and adjusting the screen to at least 1k. Interesting though, thanks for taht, I'd been on this page before (ampegv4.com) but never seen this particular page! 

~Phil

phil, not saying that you actually do need to change R50: -62V on paper will work with 6550, however, it seems that they'd be running hotter than needed. with 500V+ on G2 and with G1 sitting at -62V, to me, that would be somewhat unnerving.


--pete

[DummyLoad]

reverb board reproduction with mods to replace 6K11 tube.


reproduction main PCB


no control board reproduction though. have you found a source for the tone control tapped inductor?


--pete

[pompeiisneaks]

I'm going to have to hunt for it, but someone found that in some of the amps they  just had three series inductors instead of a single tapped one, and had the values in mH for each stage, let me see if I can find it.

[pompeiisneaks]

Found it, the V9 had the same thing but in separate chokes.  See here:

http://drtube.com/schematics/ampeg/v9pre-jp.gif

[vibrolax]

I'm going to have to hunt for it, but someone found that in some of the amps they  just had three series inductors instead of a single tapped one, and had the values in mH for each stage, let me see if I can find it.

I non-destructively reverse engineered the Ampeg multitapped inductor for my SVT preamp build.  Documentation is here: http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreampInductor.html
I bought 4 inductor cores for about $12 and a spool of #27 magnet wire for about $7.
It only took about an hour to wind the inductor.  It's easy.  No magic to the multi-tapping.

I still have the original service part I bought on ebay that I used to reverse engineer it.