How to identify tube amp

Take a picture of the back of the amp and one of the bottom, with the bottom cover removed.


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Looks like a kit to me. Maybe a clone. Your Uncle may have assembled it himself. Did he have a background in electronics?

Note the printed circuit board. That helps somewhat date the unit.
Can’t see the back of the unit, no picture. Just a guess an on/off switch and an IEC power inlet? If an IEC that would also help date, time wise, the age of the unit. Also someone may be able to age the unit by the capacitors on the circuit board.

As for the tubes used in the amp? Could somewhat try to use the tube socket pinout to some degree. Somebody with a better background than me in electronics/design may be able to tell from your picture.

I think I see a bias trim pot for the 2 power tubes. Just to the right of the fuse and left of the electrolytic blue color capacitor. A square blue color trim pot.

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surfersf OP7 posts02-09-2019 3:19pm

Closing the loop on this thread. I just returned from True Sound in Campbell. Talked to Nick Gowan who researched the pin sockets. He confirmed it’s a push-pull design that uses common tubes. He has high confidence they are EL34 output and 12AX7/12AU7 inputs. He thinks it’s early to mid 90’s, maybe earlier (he identified a cap as being built in 1985). He recommended powering up slowly (variac). @viridian, your guesses seem to be spot on!! Thank you.

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@ surfersf OP

By kit I mean the circuit board and the electronic components. It may have started with the board and a bag full of components. Your uncle may have soldered all the electronic components onto the circuit board.
If you do not have access to a variac you might want to try this.

Do you have a multimeter? Do you feel comfortable using it? If yes you could power up the unit/s without any tubes installed and take some measurements.

*** First,..... It is possible the DC voltage could be as high as 350Vdc - 420Vdc.

Because you don’t know how long the amps have not been used you should not just plug them into the wall outlet. What you can do is series an incandescent light bulb in series with the hot 120Vac line. This will work as a current limiter.

If you have an extra 3 wire computer power cord the IEC female connector end should fit the IEC inlet connector on the back of the amps.
You will need to carefully cut the outer jacket length wise about 4" to 6" exposing the hot, neutral, and equipment ground, wires. (Pick a spot where you will install the pigtail socket. Remember the light bulb will get hot to the touch.)

pigtail socket.
https://www.homedepot.com/p/Leviton-Weatherproof-Socket-Black-R60-00055-000/100356874

Next cut the HOT wire. Maybe, black, or maybe brown, or some other color.
Don’t cut the neutral wire. It is white or might be blue.
Don’t cut the green equipment ground wire.

Connect the 2 leads of the pigtail socket in series with the, (cut in half), 2 hot wires of the power cord using a couple of wire nuts.
For the light bulb use a 60 or 75 watt incandescent bulb.

If you decide you want to measure for voltages in the amps build the test power cord and then post back.
For the testing you will need to buy a couple of multimeter insulated Hook Clip probe adapters for your meter test lead probes.

Example:
https://www.google.com/search?q=multimeter+hook+clip+test+probes&tbm=isch&source=iu&ictx...:
These prevent/help from shorting out something when testing for voltages with the meter probes inside a hot chassis.

**** ALSO..... Once the unit is energized, powered on, the electrolytic capacitors in the DC power supply will be charged. Even if the unit is unplugged from the mains wall outlet the caps will remain charged possibly for many hours. If you poke your fingers around inside the unit you could/will receive an electrical shock. You will need to bleed off the DC charge off first.

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I’m not a robot.

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