Help IDing 50s amp and tubes!

[Asher]

Hi all.

this is my first post here.
i recently purchased a collection of late 40's through 50's tube amplifiers that i am trying to restore/repurpose. the two that seem most promising appear to be hi fi amps but im not sure. One is a Heathkit A-7 that the seller dated to 1953, the other, that i am looking for help with has no name and no identifying marks that i can find. Its appears to be high quality and clean under the hood. I think the power to may be bad it currently is getting no sound.

It has from what i can tell:
2 PTs, a Stancor P6005 and a Thordason (no part #)
no name OT (part # t-17 a14814)
3 12au7a tubes
1 ob2 tube
5y3 gt/g rectifier
6h6 small black tube
1 12ax7
and a non identifiable bell shapped rca power tube. with either 6 pins or 8 pins and two broken off.

this mystery power tube lights up when switched on and then dies out quickly.

the most sound i've gotten out of it is a faint hum. which started when i i tried to hook up input terminals in the back.
it have two outputs in the front 1 is 1/4 inch and 1 is 1/8 inch (WIERD!)

any idea what the mystery tube might be or what the amp might be would be greatly appreciated!!!!
or just any idea where to start with this thing. its got a lot going on under the hood i have high hopes for it!

best
Asher

THANKS for any input you can offer!

also if anyone has a schematic on a heathkit a-7
or 1953 DuKane 4C100 i am looking for those too thanks!

[Invertiguy]

Can you count the number of grids the tube has? Is it directly or indirectly heated? It's definitely octal, but without anything else to go on there's a lot of things it could be. How is it wired in the circuit?

[Asher]

Can you count the number of grids the tube has? Is it directly or indirectly heated? It's definitely octal, but without anything else to go on there's a lot of things it could be. How is it wired in the circuit?

i cant count any grids the tube has 3 wires that go through a plastic insulator into a tin can. It glows violet but then seems to die down.

the amp also has unusual inputs on the back each with 3 slots, (2 horizontal, 1 vertical) and on the front we've got a 1/4 inch out and an 1/8 inch out (as far as i can tell?) any idea what this amps function is?

[Asher]

the mystery tube appears to be an Oa3 or similar tube. The function of the amp remains a mystery.

[Reeltarded]

I have never seen and unmarked RCA from that era and you have not looked very closely at the very top of your tube.



I am guessing...

I think it matches the 0C3 rectifiers in my Leslies. That is a Leslie chassis.

[martin manning]

0A3, OB3, OC3 are voltage regulators, cold cathode gaseous discharge type. Try putting it in the freezer for 5 minutes or so and then take it out and breathe on it. Sometimes the markings will show up.

[Reeltarded]

Tricky!

[Asher]

no luck putting the tube in the freezer, or looking at it with an LED flashlight or in sunlight. Dont know if there are and other tricks.

I think it matches the 0C3 rectifiers in my Leslies. That is a Leslie chassis.

Hi reeltard, are you sure its a leslie chasis?

i'm starting to entertain the idea that this is a compressor/limiter? possibly. I've traced the circuit as best as i can and am working on a drawing of it. but there is no power stage here just pre-amps, regulators, and rectifiers. The 3 knobs on the front is why i said compressor. (Which would be an amazing find...

Here is a photo of the back. any idea what these jacks are for?

[Reeltarded]

The chassis is screaming leslie at me. it's been built into something completely different but god only knows without looking at the circuit.

It appears to possibly be some sort of line amp for maybe a remote PA feed but I am not good enough to see anything obvious.

The OC3 and placement of it are typical of the couple i have with that tube, the next small nine pin is an AU7 on a Leslie, and then i get lost and wonder where the power section is but I have no intrest in models other than 145 or 122 so i don't know what the heck it is.

can we see the back and that last side?

[Asher]

That seems to fit. The Oc3 feeds into both the OT and into a small Au7 size socket. The seller had popped an Ax7 in that spot. But there are 3 au7 in the "input" or "preamp" section of the circuit (if thats what it is). so i was suspecting that it is also an au7 in that spot at the end of the chain by the OT.

can we see the back and that last side?

sorry which side do you mean?

thanks for all the feedback

[Reeltarded]

I looked around and googled 6h6 plus Leslie amplifier and got nothing.

Fun though!

[Asher]

leslies seem to always have a ins/outs on the side of the chasis. there are no extra holes on this guy...

[Asher]

this is driving me crazy! i might have to break down and take it to a tech who specializes in gear of this era.....

[Reeltarded]

Hammond B3 and the other tonewheel organs from that period have internal preamps that feed the Leslie. There are several other companies that used Leslie, like Conn, to make amplifier sections for their organs as well. Some of these had a preamp section built by Leslie.

It has been painted and repurposed, but I think 90% it is a Leslie product on it's birthday. With two inputs and the.. what is that middle knob for..

Looks like a tube line amp because I can't imagine any other reason. What the heck does it do now?

those jacks are the common speaker outputs for a single section rotating speaker, fast/slow which means the relay is separate and with the cabinet.

Speculation out on a limb. I'll take this bet.

[Asher]

thanks for your input!