Sony Tube R2R TC-500A - Zero Sound Output on one channel

corpblues

AK Member
I picked up a Sony TC-500A in a deal for 5 R2R plays. It appears to be in great condition (expect for the issue on one chanel) and appears that someone may have even restored it in the recent past.

In searching the internet for details I came across this might be the model the Bob Dylan Basement Tapes was recorded on. This might be fact or internet rumor.

One of the two channels has no sound output. I tested in both play and record modes. I assume the issue will only require a basic repair due the very clean internal condition and all tubes glowing the issue is probalby minor.

The mechanicals are working for me fine.

I did swap the tubes from one side to the other, but the problem did not follow the tubes. Seems like a broken connection somewhere but I don't know how to find it.

Anything obvious and simple I should check? I know tube stuff can be dangerous to mess with.
 

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First thing is to know if the problem is with the deck or the amp. Once that is determined then you can work on the problem with a good idea on what to check.
If you have already determined that the amp is the fault , try to take measurements of voltages at critical points in the amp. You should have a schematic which should give you voltages at the critical points of the circuit. Alternatively, you can check the voltage on the good side and measure the exact same point on the other channel.
 
http://audiokarma.org/forums/index.php?threads/tell-me-about-the-sony-tc-500a.461370/
Hifiengine has a service manual for it: https://www.hifiengine.com/manual_library/sony/tc-500.shtml
Why does it have "Electro-Harmonix" tubes in it? Someone's been fiddlin' around inside of it.

Standard troubleshooting. Looks to be a two head deck, so no issue with dirty SOURCE/TAPE monitor switches, right?
When you say "zero sound output", what does that mean? The 500A is a full tape recorder, as I understand it, with amplifiers and loudspeakers(?).
Do you have the speakers and are they hooked up? Do you hear anything from the "nonworking" channel's speaker? Hiss, hum, or nothing?
If the latter -- bad speaker cable, perhaps?

If you feed a line level signal into the line inputs (both channels), set the deck up to 'record' and turn the line input levels up, do both VU meters 'dance'? You should get the sound out of the line level outputs and/or the speakers -- have you tried monitoring both ways, with no sound from one channel even from an input signal (as opposed to playing back a tape)? You should (I think) be able to do such a test even with the deck in "pause" mode (I reckon it has one, probably just mechanical?).
 
By zero sound output I mean zero sound at all. The channel 2 VU meter does not dance at all. I could get a little static from when turning the volume/input knob before I deoxit the pot, that is the only noise at all. I switched speakers and tubes from channel 1 to channel 2, so I know those components are not the issue. I can put it into record mode and use a MIC to test, channel 1 works fine but channel 2 is dead quiet.

I think someone restored this unit at some point. It is too clean inside to not have been fully serviced at some point. The belts are also good. I obtained this R2R in a lot of five R2R decks from a friend in the hobby of selling LP's. He bought these along with about 2,000 records in east Texas.

Since it is in such nice condition and beyond my skills I am just going to list it for sell. Hopefully it finds a good home. I don't want to risk shorting something out due to my novice electronic skills. I did find in researching that some people use these to turn into tube monoblock amps.

Appreciate the suggestions.
 
Looks to have two small single ended .amps, with 6AQ5 audio output tubes. Probably best left in the recorder, if you just want a stereo tube amp.
 
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