Building a Ampeg V4, questions about changes

[Balticnoiseforge]

Note: Iam not a designer guy and has quite limited knowledge around the theory of amplifiers, but have built quite a few and some from the ground up without schematics with guidance from valvewizards page.

Building a Ampeg V4 clone?

Have in last years built several amplifiers and would like to build something abit more complicated, and always wanted a Ampeg V4.

But looking at their schematic i see some stuff that could need some changes if building the amplifier from the ground up.

So any repair guys here that could mention stuff in them that can be a cause of concern?

Two Channels

The main things iam looking at is obviously  ditching the polarity/standby switch and those oddities.
But for the schematic i linked i dont see any difference between the channels? Are they ment to be voiced the same?
For that reason i had a thought about doing one distortion model channel and one standard.

With the distortion preamp i have a question about what optoisolators where used if someone know? Also if building that a bypass for the clipping diodes would be nice to have.

Preamp RC filters

But main thing i found odd in the amp is the filtering, the whole preamp comes from the same filter stage, if building it new would it be a good idea to try get a few more filter stages in but still try keep voltage not to far from the original?

Also instead of having a resistor outside the filter network for the screen grid that may be omitted for a choke instead to give better filtering for the rest of the amplifier?

Phase inverter

Also iam not the best theory guy, but to me it looks like the phase inverter could have been designed better, i intend to use a PPIMV instead of their classic Master volume after the FX loop, but i cant put finger on how you could improve it. So any suggestions would be appreciated.

Input Jack values

The ampegs got their unusual 5m6 and sometimes 1K / 50pF - is the 50pF tied to cathode for noise reasons? And could it be better to use a 1meg / 10K / 50pF to ground configuration?
Or is their unusual way part of the sound? Just feels like 5m6 is unecesarry large.

Reverb circuit

Heard alot different about their reverb, both good and bad - obviously subjective, so just wondering what people think about it.
And if it actually aint that good then maybe use of another reverb circuit with a driver?
 
That is some of my thoughts about it for now, If anyone that have worked at alot of ampegs Id appreciate any input about my ideas or other stuff.

[PRR]

> always wanted a Ampeg V4.  But looking at their schematic

Yes it is complicated.

You say you want a V4 and then you have a long list of things you do not like?

The ONE thing I would "have to" change is the 540V on the screens. That was insane, even on the optional 6550 finals. And as Ampeg iron is rare or costly, and at 120 Watts(!!) a power amp is a power amp, _I_ would steal a Fender or Marshall power stage and iron.

Mind the weight! The 60W VT-40 combo was a complete pain to move.

I never met a musician who understood Ampeg's fancy mid-EQ. I sure would not double-up on that.

You may be well-served building a Bandmaster into an Ampeg case.

[Balticnoiseforge]

> always wanted a Ampeg V4.  But looking at their schematic

Yes it is complicated.

You say you want a V4 and then you have a long list of things you do not like?

The ONE thing I would "have to" change is the 540V on the screens. That was insane, even on the optional 6550 finals. And as Ampeg iron is rare or costly, and at 120 Watts(!!) a power amp is a power amp, _I_ would steal a Fender or Marshall power stage and iron.

Mind the weight! The 60W VT-40 combo was a complete pain to move.

I never met a musician who understood Ampeg's fancy mid-EQ. I sure would not double-up on that.

You may be well-served building a Bandmaster into an Ampeg case.

Long list of things i want to change? No wouldnt want to change the sound to much, but like you say the poweramp have very high screen grid that could be lowered.

That the whole preamp shares same RC filter also feels abit weird, splitting it into atleast two wouldnt make that much of a difference soundwise - but would probably be less noisy and get better filtering.

And having option to use their distortion channel and normal v4 channel in same amp.. why not if building it from scratch?

And why would i build a bandmaster into a Ampeg case? Trying to be funny? If not no i dont want to build a bandmaster, recently built a Fender 6g6b with Bassman transformers so not a fender again.

Also if building a Ampeg i wouldnt want a chassi with tubes mounted downwards like original.

[Keppy]

Two Channels

i dont see any difference between the channels? Are they ment to be voiced the same?

It sure looks that way.

For that reason i had a thought about doing one distortion model channel and one standard.

Beware of any changes that affect the biasing of V1b and V2b. Those stages are connected plate-to-plate with no mix resistors or coupling caps, so what affects one affects the other.

Preamp RC filters

But main thing i found odd in the amp is the filtering, the whole preamp comes from the same filter stage, if building it new would it be a good idea to try get a few more filter stages in but still try keep voltage not to far from the original?

There's already four stages of filtering in there. I doubt you'll see much improvement.

Phase inverter

Also iam not the best theory guy, but to me it looks like the phase inverter could have been designed better, i intend to use a PPIMV instead of their classic Master volume after the FX loop, but i cant put finger on how you could improve it. So any suggestions would be appreciated.

That's a floating paraphase inverter. Check out the bottom of this page: http://www.valvewizard.co.uk/paraphase.html

Reverb circuit

Heard alot different about their reverb, both good and bad - obviously subjective, so just wondering what people think about it.

My experience with Ampeg reverb is that it's "rich" rather than "splashy."

[shooter]

I'd borrow my buddies modeling amp when I needed "that sound"




IF you're all in, come up with a bullet-proof layout, something already designed n tested is a +

[DummyLoad]

I own one of these - Agree the mid shaping is a bit excessive, but entertaining in any case.

The 50pF from grid > cathode is there to shave RF.


540V to the screens is not as bad as 100W UL conditions for a 6550. I am running Groove tubes 6L6CG-GE that were available for a short while. I have a small stash of NOS 7027 as backups. Eventually, I'll probably make the minor mod the bias PS and use 6550/KT88.

Build both channels, build the pre-master vol. version, IMO it sounds MUCH better - Use a decent pedal for distortion.

I added a B+ fuse to mine and improved the PS. Mine was bought literally as a basket case with blown OT. Fiptops provided a Heyboer clone. Awesome sounding amp.

Love the Ampeg reverb. So has anyone that has dropped by to give it a test drive. The only thing is that the 6K11 Compactron tube. There are becoming more scarce. There was a man in Austria that had replicated the PC boards and redesigned the Echo Board to use 12AX7/12DW4 rather than the 6K11 Compactron. Don't know if they are still offered - Check Ebay, that's where I found them. My amp is still stock and I have some spare compactrons. I was going to redesign that board myself eventually, if/when I run out of 6K11 replacements.

I own an early version VT40 as well, and love it. My three go-to amps are the V4, VT40 and a 67 Super Reverb.

Links below to some photos of how the V4 and VT40 were received through the restoration of both.

V4:
https://www.dropbox.com/scl/fo/ineywbezlvbllu6tp0x8d/h?dl=0&rlkey=g8iv7evfj3g57evd2nfykpe3u

VT40:
https://www.dropbox.com/scl/fo/ineywbezlvbllu6tp0x8d/h?dl=0&rlkey=g8iv7evfj3g57evd2nfykpe3u


--Pete

 

[tubeswell]

If you're after the Ampeg V4 sound, you definitely have to build the V4 preamp with the tapped coil. That just gives any bass guitar an awesome dynamic range. I love that sound. If you don't keep that entire pre-amp, you're screwed and you might as well build a bandmaster as PRR said.

[Balticnoiseforge]

If you're after the Ampeg V4 sound, you definitely have to build the V4 preamp with the tapped coil. That just gives any bass guitar an awesome dynamic range. I love that sound. If you don't keep that entire pre-amp, you're screwed and you might as well build a bandmaster as PRR said.

What i ment with that was simply instead of having the channel 2 on the standard non distortion V4 to replace that channel with the distortion models preamp, but having them both connect similiar to the 68K anode 3K3 triode.

[Balticnoiseforge]

Thanks for all the insight, but both your models are non distortion right?
If you tried their distortion models - what do you think about them?

Having a distortion models channel and a standard V4 one seems totally possible?

Also thanks for suggestion about how to replace the 6K11 tube and your good words about the reverb.

I suppose cloning it straight is the best way to go about it as usual.
But may i ask what changes you did to the PSU? Was it just fusing and taking away polarity stuff and such?

Thanks!

[Balticnoiseforge]

If you're after the Ampeg V4 sound, you definitely have to build the V4 preamp with the tapped coil. That just gives any bass guitar an awesome dynamic range. I love that sound. If you don't keep that entire pre-amp, you're screwed and you might as well build a bandmaster as PRR said.

What has a Fender 5e7 in common with a Ampeg V4?
I Obviously did not mean to change whole preamp, it was a thought about using the standard v4 channel input AND instead of the exact copy of channel 1 try make it work with the distortion input from their distortion models for channel two.

But with minor modifications like clipping diode bypass.

So using the standard V4 input on the schematic on top of thread but using the channel 1 input from this schematic as channel 2.

Schematic of distortion model below.

[J Fletcher]

 I smell an opportunity here ! Maybe I can make a deal ! Have two original power transformers for these Ampegs . Have had them for 25 years or so . Think they used the same PT in the V4B and maybe one or two others . I built a bass amp using one of them , high voltage came in around 500 vdc by the way . Realistically , they are heavy , shipping would be killer .

[Balticnoiseforge]

I would suppose you are from America right? Since they were mostly from there - since iam european that sadly would probably be way to expensive, also paying alot for a power transformer doesnt make much sense - if it were a OT it would be different.

 And also there is power transformer / output transformers for the V4 for decent price on thetubeampdoctor, probably not exact replicas but should do the job.

[dude]

If anyone is interested I have a V4 Head 1970's, I think 1974, in very good condition, has Distortion.  Not currently playing, needs more maintenance. All knobs, grill cloth in good shape. Many parts replaced, new filters, new FlipTop PT, it's all there. PM me if anyone is interested, will sell cheap but can't ship, 60 lbs at least. Zip 19063 for p/u.
I'll put this in stuff for sale but seems relevant to post here..?

[Balticnoiseforge]

Very sloppy and fast drawing, but it is pretty much like that i imagined when saying having both V4 channel and distortion channel. With rest of circuit being the normal V4

[owen]

to OP, the ampeg v reverb was always so much better sounding than fender amp reverb to me, and I’m a reverb junkie. less dark, less pronounced relflections on the ampeg. very hifi/rich sound. Also, i had a distortion model and did not like it. My non-master volume one was the winner. my master volume one wasn’t my favorite either.

> always wanted a Ampeg V4.  But looking at their schematic at 120 Watts(!!) a power amp is a power amp, _I_ would steal a Fender or Marshall power stage and iron.

I never met a musician who understood Ampeg's fancy mid-EQ. I sure would not double-up on that.

I love the mid control and used it judiciously on my ampeg V amps. I wish more amps had such a fantastic eq circuit, I would select different center frequencies, personally.

I’m not OP, but I’m looking at building a v4 front end with even more power to squeeze out the headroom and LF handling.

[Balticnoiseforge]

to OP, the ampeg v reverb was always so much better sounding than fender amp reverb to me, and I’m a reverb junkie. less dark, less pronounced relflections on the ampeg. very hifi/rich sound. Also, i had a distortion model and did not like it. My non-master volume one was the winner. my master volume one wasn’t my favorite either.

With all those reverb comments its definently a keeper and something i want to try out - but when it comes to master volume, do you really think a PPIMV would draw it back? Their normal master volume is wired quite abit different - a master volume is always nice in the end.

But in a standard V4, is there any reason to switch between jacks since they are ultimately the same?

That is why i thought about adding distortion channel, but not the distortion models "non distortion" channel but the V4

[PRR]

The factory plan for the Distortion channel has an error in it.

The "Distortion" was awful, like a cheap transistor.

[Balticnoiseforge]

The factory plan for the Distortion channel has an error in it.

The "Distortion" was awful, like a cheap transistor.

I got no experience of how it sounds but either way - what was the error in the factory plans?

[PRR]

.

[Balticnoiseforge]

.

Ah yeah that i should have noticed, thanks!

[DummyLoad]

Thanks for all the insight, but both your models are non distortion right?
If you tried their distortion models - what do you think about them?

Having a distortion models channel and a standard V4 one seems totally possible?

Also thanks for suggestion about how to replace the 6K11 tube and your good words about the reverb.

I suppose cloning it straight is the best way to go about it as usual.
But may i ask what changes you did to the PSU? Was it just fusing and taking away polarity stuff and such?

Thanks!

Correct, both are non-distortion, both do not have the master volume.

I added a bit more filter to power tube plate supply and the screen RC network. Made the screen supply rail a stack with balance resistors. I did this on both amps; the V4 and VT40. I added a 1A FA fuse to the B+ supply of the V4.   

Agree w/ Tubeswell, the mid shaping is part of the appeal of the amp but not necessarily the whole appeal of the amp. The mid multi-tapped inductor was available as a replacement for a while from Loud Technologies, but I've read elsewhere that's no longer the case. Cinemag will wind one for you.

Not a fan of the diode pair clipper for the distortion channel. There are pedals available that sound 1000x better than that channel. Respectfully, that's just my opinion.

--Pete

[Balticnoiseforge]

Thanks Pete for all the info!

The more i hear about the distortion channel it feels like a bad idea, so i will probably end up doing the 70s V4 version but still try have a ppimv in it.

And yeah ofcourse i will have their inductor mid circuit, except i will ditch the 6K11 tube.
Will order a custom one, so thinking about adding a few more inductor values and have them on a rotary switch.

With your PSU did you end up having aprox 100uF for the B1 and somewhere of 50uF+ to the screen grid? Instead of the standard 50uF to B1 and 40uF to screen grid?

[DummyLoad]

For the early model V4 I have: Stacked a pair of 2x100uF 500V cans strapped the 2 sections in parallel for plate supply, so, yes, 200uF in series with 200uF=100uF total. For the screens, I stacked a pair of 100uF 450V radial caps in series so, then yes, 50uF for screens.

See schama attached for clarification. I didn't document what I did at the time, so I guess now is a good time to scratch that off the long list of things needing to get done that aren't getting done... 

Link to schema of the V4 I modded: https://www.dropbox.com/s/jjjrcce2wn2khq4/Ampeg-V4_June-1970-schema.jpg?dl=0

--Pete

[vibrolax]

I built an SVT preamp using a Hoffman-style turret board layout that I created from the factory schematic.
It includes the infamous semi-parametric midrange circuit with the multi-tapped inductor.  I non-destructively reverse engineered the inductor from a genuine Ampeg service part, if you want to wind your own.

It's all documented at http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreamplifier.html

Jon

[Balticnoiseforge]

I built an SVT preamp using a Hoffman-style turret board layout that I created from the factory schematic.
It includes the infamous semi-parametric midrange circuit with the multi-tapped inductor.  I non-destructively reverse engineered the inductor from a genuine Ampeg service part, if you want to wind your own.

It's all documented at http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreamplifier.html

Jon

Hey vibrolax! Sorry for late reply - yes ive seen your page and have taken great help from it!

Ordered stuff to wire one, but sadly i ordered to small ones but with similiar nH since the FT-87a-j was really hard to find in Europe, and ordering from it the states would be like buying a finished one from Mercury. Bought a ft-50a-J and some others but yeah.. small 😅

But hopefully i will find something similiar, if you know of any id be happy if you could give a clue. ( That is carried by mouser or similiar. )

[Balticnoiseforge]

When you talk about dc resistance in your article, is that measured when it is in circuit? I wired up a toroid to 100mH and with a standard ohm measurement it measures 2.2k at 120hZ.
Using 0.4mm wire, but toroid have unknown nH value.