2x6J7, 6L6, 5Y3...Sound Familiar?

[soundguruman]

I have a mystery running this tube set. Does anyone know of some amps that use this configuration? We're searching for schematics.



It's definitely a home brew, but I'm hoping he built it using a known circuit.

EG

It's a Valco, (AKA Oahu), but a later prototype, that does not have a field coil speaker. Could have been an unfinished one, or one that was built out of Valco parts, but mostly Valco. Late 1940's after they stopped using field coils. Without a doubt, a Valco Chassis. They also manufactured these for National.
Just for trivia sake--- you are looking at a guitar amp design that predates Leo Fender. Leo is said to have invented the first guitar amp, but we know from examples built by Valco and Rickenbacker, that this simply is not true. Valco and Rick guitar amps came about 10 years before Leo built his first (or even earlier). The original face plate (now missing?) had inputs labeled: "Microphone or Instrument," and therefore, "instrument" input makes it an actual guitar amp.
The Valco 51 which is quite similar, with a field coil speaker, is probably one of the sweetest sounding amps ever made. At least I think so.

http://www.valcopages.com/Schematics.html

[Elias Graves]

Awesaome! Thanks for the info!

EG

[soundguruman]

You will need fudge a bit, because they made sooooomany different models...
However what you have there is one of the first guitar amps, historically speaking.
I recognize the original cabinet but it's been recovered...
At the time, there were no efficient loudspeaker magnets, and loudspeakers were quite heavy because of the iron magnet.
In the mid 1930's the idea popped up to route the high voltage through a field coil, and the coil was an electromagnet for the speaker.
The coil basically replaced the choke of the amplifier. This magnetized the speaker frame, and a lightweight speaker became possible.
I can't tell if your speaker has the extra coil from the photos..but it looks similar.
Anyhow, at that time, Rickenbacker had invented the first single coil pickup, and it was sold on a frying pan shaped guitar.
Suddenly, lap steel guitars became amplified, in the late 1930's. Rickenbacker probably made the first guitar amp, soon followed
by Valco. The first Valco amps appeared in the early 1940's. I have worked on two that were built in 1941. But this was not the first
Valco Model (the 51). There was at least one previous Valco model which I have never seen in person.
Leo Fender worked for Rickenbacker as a technician at the time of the first guitar amp. His first amp showed up at least 6 years after
the Valco guitar amp went into production.
Therefore, Leo DID NOT invent the guitar amp. What you have is an amp that probably predates Leo. However it also looks like it was never
finished. There were no 1/4" jacks at the time, and your amp probably had the jacks added at a later date.
That's what's cool about it, it looks like an unfinished Valco prototype.
So anyhow on your amp, the output tubes ARE the phase inverter. There is no dedicated phase inverter tube. This indicates that it is
a very early model, I'm guessing 1940. This may be the first model Valco amp, that was never finished. I have never seen another one like it.
But I have seen the schematic to it.
And so, long about 1940, Valco shoots off to produce amplifiers in Hawaii. This was the Oahu amplifier, that is the same as the Valco, except
that it has a palm tree stenciled on the grill cloth. (very cool looking). Exactly the same amp, with a different nameplate.

[Elias Graves]

So, is this amp potientially of historical interest? Should I have it seen by a Valco specialist?

EG

[soundguruman]

So, is this amp potientially of historical interest? Should I have it seen by a Valco specialist?

EG

I don't think there are any left alive.

[Elias Graves]

I don't think there are any left alive.

Hahaha! I meant a Valco amp repair specialist.

EG

[J M Fahey]

Yes. He too.

[soundguruman]

Hahaha! I meant a Valco amp repair specialist.

EG

I think there's not many of those left either.
You want to look at the speaker and see if there is more than 2 terminals..maybe four or five?
If it does have more than 2, you have the pre-1940 field coil speaker, which sounds very nice.

[Elias Graves]

Well, the burning question, I guess, is how much should I be willing to spend to get it going? $300? More? Less?

EG

[Elias Graves]

This is the amp rhodesplayer refers to, look at the iron and compare it to what you got.






As he duly noticed, the PT looks very good; the OT a very undersized one, typical of what you would find in a table radio, similar to what tubenoob is trying to recycle.
I think that by replacing it for a proper one and tweaking a little, you will have a killer amp in your hands.
You already have the killer speaker !!!!!

Ron called and said this looks like the same circuit. He's gonna start comparing and checking out components.

A couple of things neither he nor I understood were those screwdriver pots and the odd input arrangement. There are two unlabeled plugs that face the front and one in back that seems to lead to the screwdriver pots.
Hopefully, this will make some sense of it.
Thanks.

EG

[J M Fahey]

I guess $300 would buy a lot of (other) amp.
jm2c