Tx-200 uneven voltages and strange happenings

[Carbsandcaps]

Working on a tx-200 that I received in no working order. I’ve got it all recapped and replaced the output transistors. Some questionable resistors and set the bias the 135mv on each set. When it’s on below half volume it sounds wonderful. When you start to turn the volume past that it’s start going crazy. The sound starts pulsing along with the stereo light. I assumed this was due to the 6800uf caps I put in place of the 2000uf and the transformer couldn’t keep up. I put some 2200 in and still does it.

I also noticed that the positive voltage out of the diodes is 32v and the negative is -39v. When the distortion starts the positive goes even lower and the negative goes up to -42! The voltages are supposed to be 35ish each. There is a 7 watt resistor that goes from the negative output to ground. Going from 180ohm to 150 seemed to help a little bit but still does it. It will also do this with no music being played just the speakers hooked up. It goes thump thump thump. I assume the big resistor is suppose to balance out the voltages since the positive side is running basically everything that isn’t the outputs.

Anyone got any ideas or know what the heavy resistor’s job is! Thank you.

 

[larryderouin]

Schematics would help as the TX-200 is one of those RARE BIRDS, that almost no one has heard of much less seen. And the manuals are even harder to come up with. TX-200 dates from 1965-66 and would be 1st gen S.S. for Fisher.

 

[Carbsandcaps]

Schematics would help as the TX-200 is one of those RARE BIRDS, that almost no one has heard of much less seen. And the manuals are even harder to come up with. TX-200 dates from 1965-66 and would be 1st gen S.S. for Fisher.

Here’s the power supply with the resistor in question. I can get more pictures if needed. Voltages are still off with all 8 output transistors out too.

 

[larryderouin]

Pull each of the output's in turn and make sure they are viable. 6 way test https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/ germanium transistors may read a little lower than silicon. Also check emitter resistors. Thinking is something is loading down Negative side (possibly) or having a breakdown on Positve side as volume/power increases.

Voltages on AA, BB, CC, DD, EE. Selector to AUX, Volume to minimum, tone controls off or centered. No sources connected. Spkrs connected and spkr switch on.

Please scan the whole manual and send the scans to https://audiokarma.org/forums/index.php?threads/please-help-the-ak-database.349095/

 

[Carbsandcaps]

Pull each of the output's in turn and make sure they are viable. 6 way test https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/ germanium transistors may read a little lower than silicon. Also check emitter resistors. Thinking is something is loading down Negative side (possibly) or having a breakdown on Positve side as volume/power increases.

Voltages on AA, BB, CC, DD, EE. Selector to AUX, Volume to minimum, tone controls off or centered. No sources connected. Spkrs connected and spkr switch on.

Please scan the whole manual and send the scans to https://audiokarma.org/forums/index.php?threads/please-help-the-ak-database.349095/

Ok I’ll check on that tomorrow I did check voltages with the outputs out and same thing. I’ve set the bias but not with speakers connected. The positive supply is split and goes off to power the driver circuit and preamp/ tone controls. Then that all goes to ground. I assumed the 180ohm resistor was there to make up for the negative voltage not being used for anything but the outputs.