• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

recognize this old amp?

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Hello trigger, I cannot tell you what brand the amp is or what it came out of. I can tell you the guys description of the tube types is wrong on at least two of the tubes. There is no 6AV6 or 6CA4. The 6CA4 is a nine pin rectifier and this amp has an 8 pin rectifier tube which is most likely a 5U4. Mickeystan
 
Trigger,

That almost certainly came from a console. When you have the unit in your hands, look for a power connector that fed a tuner/preamp.

I'm guessing the circuitry in that chassis is a "concertina" phase splitter for each channel into a pair of PP "finals". I agree with the 6BQ5/EL84 O/P tube assessment.

If my circuitry guess is correct, the "beast" could be made "self contained" by using a 12AX7 to form voltage amplifiers for the 2 channels and installing MOSFETs to take on the "concertina" phase splitter duties.
 
Trigger,


If my circuitry guess is correct, the "beast" could be made "self contained" by using a 12AX7 to form voltage amplifiers for the 2 channels and installing MOSFETs to take on the "concertina" phase splitter duties.

thank you much for your well informative response.

this is my first dabble into a concertina, so please bare with me.

so without a double triode or mosfet to feed the concertina circuit there will be no gain?

i will research this for the next few days. is there a simple mosfet circuit that can easily be applied in general push pull amp applications?
 
thank you much for your well informative response.

this is my first dabble into a concertina, so please bare with me.

so without a double triode or mosfet to feed the concertina circuit there will be no gain?

i will research this for the next few days. is there a simple mosfet circuit that can easily be applied in general push pull amp applications?

The pre-amp section chassis had the actual VA driver and then that was cabled down to the splitter tube. By the looks of that amp, the best route would be to strip it for the iron and tubing and start a new build, chassis and all.
 
a complete rebuild would be fun and ideal yet i feel that would be a bit more than i can handle at the current time. being a long time running noob, i have no second eyes with electronics available, using the net as a learning tool only, Ive just never run into anyone interested in audio electronics. so far i have worked with several old pulled amps, made them plug and play, recapping... last winter i assembled a tda7294 feebay kit.

maybe i should give it a try. cabin fever is setting in and my home theater is a cheep china 4ch powered subwoofer,...lol
 
a complete rebuild would be fun and ideal yet i feel that would be a bit more than i can handle at the current time. being a long time running noob, i have no second eyes with electronics available, using the net as a learning tool only, Ive just never run into anyone interested in audio electronics. so far i have worked with several old pulled amps, made them plug and play, recapping... last winter i assembled a tda7294 feebay kit.

maybe i should give it a try. cabin fever is setting in and my home theater is a cheep china 4ch powered subwoofer,...lol

There is room on the corner to add a driver tube. But this one won't be as simple as adding some RCA jacks and a switch and a recap.
 
There is a circuit type that you could build on this chassis without adding a driver and socket. It's called a self-inverting push-pull, and you would rewire the existing inverter socket to take the driver tube and that's all you'd need. Apart from the gut job. Those output trannys look to be UL, too. On the bright side, you got your money's worth on the parts, if they're all good.
 
I'm betting that this is an old Magnavox amplifier from a console stereo.
It's not a Zenith. Back then, Zenith copper-coated the inside of their chassis.
I once owned a Magnavox mono amplifier which was built on a very similar chassis.
It used a 5Y3, 12AX7 and a pair of 6V6 tubes.
This amplifier might be worth a rebuild before you dismantle the original amplifier and use the chassis to build another. The performance may surprise you!
 
what would be more simple, adding a driver tube or adding transistors for phase splitting?

That depends, at least in part, on how well set up you are to do sheet metal work.

I'm no fan of BJTs, but FETs are a very different story. A FET is darned close to being a heaterless pentode. :) FETs work well in "unity" gain situations, like voltage followers and split load ("concertina") phase splitters. :D Enhancement mode "N" channel parts are extremely easy to DC couple to tube plates.

Let's say, for sake of argument, that a 12AX7 section will be the voltage amplifier. The FET to use is the ZVN0545A. Even the wimpy 'X7 triode has no problem in driving it's tiny capacitances.
 
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