VOM Amp 20053 suggestions

Rex Everything

Rex Everything

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I've got a cool little console pull Voice Of Music amplifier model number VM 20053 . I like my 6AQ5 integrated so much I decide to pick up this EL84/6BQ5 based amp and matching pre amp.

I was just looking the amp over and making plans to recap it and replace any needed resistors and I thought I'd consult with the folks here and see if there are any improvements that should or could be made to the circuit to make it a better sounding, stable amp.

Here is the schematic. I'll post the pre amp schematic also in case anyone has any input on it.

Thanks :thmbsp: :music:

VM 20053 Amplifier:

VOMschem2.jpg


VM 20026 pre amplifier:

VOMschem.jpg
 
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I don't think I've seen many amps split up this way, with the power amp's input and global feedback loop reaching the preamp chassis through separate cables. The preamp might be 'voiced' for its intended speaker setup. I would measure frequency response and then decide whether to meddle.

Do ya feel better now? :D
 
BinaryMike said:
Do ya feel better now? :D
Click to expand...

LOL! Kinda :D

Thanks Mike. This can go stand alone as well but thought it might be cool to use it with the pre just to keep it together (and I like the VOM sound)

I've not heard it yet but suppose I could have a listen as is before diving in.
 
Maybe I should expand discussion of my previous statement: This power amp is incomplete without the preamp chassis -- its input stage would be missing.
 
I run a VM el84 amp that I pulled from a console.
I use it with an NAD 1155 preamp.
This preamp works well because it has inputs for low-level amps.

I'd be curious to know if others have made tweeks with the design to get the final amplification level without the need of the VM preamp.

As for the sound of the amp: It sounds excellent.
I replaced the original ceramic coupling caps with 716Ps and ALL the electrolytics.
I'd put the amp up against any el84 amp Motorola or Magnavox built.
 
To be honest Rex, that is about the worst circuit I've seen in these console pulls. IMHO.
If it were me there wouldn't be much left if anything resembling the original circuit there.

I'd be going for an whole hog new design.. (not a paraphase fan, an with it in the pre to)
That is me though, I rarely leave stuff stock an like tinkering where I believe benefits are.

Just to give my perspective an 2 cents worth.. ;)
 
I was also looking at that NFB arrangement. Having parts of it located on different physical chassis is sort of different. I also can't say I've seen a setup quite like this with the resistor from plate to cathode on the output of the pre-amp. What purpose does that serve, a local feedback loop for that specific stage within the global feedback setup?
 
It's a "floating" paraphase circuit, with the first triode in the end of the preamp section.
(take a look at an paraphase circuit say from a maggie console an see the basic setup)

And that resistor isn't really from the Plate to the cathode, But from Supply to Cathode
to "bias up the triode" so to speak.
 
You Could, relatively easily change the amp section to a concertina splitter an
use that last triode in the preamp for your voltage amp tube with some tweaks.
 
Kegger said:
You Could, relatively easily change the amp section to a concertina splitter an
use that last triode in the preamp for your voltage amp tube with some tweaks.
Click to expand...

Well...I'm just a parts swapper so a lot of this has gone over my head but I get the "key" points.

It sounds like it's finally time for ol'Rex to learn how to build from scratch ;)

Guess the correct place to start would be to figure out an easy circuit that will not cost a bunch to build.
I really was hoping this would be like my 1448 but if it's all gotta go then it's all gotta go :D
 
Then taking your schem and modding the amp section (compare A channel to B channel)
(I reworked the top channel to show the circuit changes, and blew it up)

You can see how the makeup would change, now compare that to the other one I posted.
(and you can see how the first triode section coming from the preamp would look as well)

attachment.php


This is just for your info, I'm not telling you to do this nor am I saying try an figure a whole
new driver section out for yourself, but look at those 2 an see how they differ, but are also
not that far apart as far as parts count and makeup is concerned that you could see how it
could be implemented if wanted without to much of a reworking there. (food for thought) ;)
 

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i have the same console pull amp. i call it the killer because it sounds better than expensive amps. i re-capped mine and used oil filled caps for my coupling caps. a true sleeper and getting harder to find!
 
Kegger said:
Then taking your schem and modding the amp section (compare A channel to B channel)
(I reworked the top channel to show the circuit changes, and blew it up)

You can see how the makeup would change, now compare that to the other one I posted.
(and you can see how the first triode section coming from the preamp would look as well)

attachment.php


This is just for your info, I'm not telling you to do this nor am I saying try an figure a whole
new driver section out for yourself, but look at those 2 an see how they differ, but are also
not that far apart as far as parts count and makeup is concerned that you could see how it
could be implemented if wanted without to much of a reworking there. (food for thought) ;)
Click to expand...

That looks like just a couple parts difference. Am I looking at it right? I need to look a bit more at the pre amp section
 
Yes look over this one, look over the one I linked to, read my following post on the
other one and look at this preamps last triode an how that would fit into the circuit.
(take some time and digest it, an you should see how they all interconnect then) :)
 
Yes, concertina, cathodyne an split load are all the same phase splitter, just the name.
(can be AC or DC coupled from the previous stage with proper "bias" setup)

This amp originally used a floating style of the paraphase splitter, myself on these easy
to drive tubes I prefer the direct coupled VA to Concertina splitter/driver above all else.

-----

That is just My preference, from experience, technical an sound, I Prefer that circuitry.
 
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