TU 8200 lost left channel

[Rdugg]

My TU 8200 DX performed flawlessly for 4 years from the first time I turned it on. I use it daily in my office.

The left channel died due to a tube failure. Now I can't seem to get bias voltage at pin 8 or 1 of the tube. It is correct at the base of the transistor then acts like a short to ground. Each component tests correctly. The tube also only heats up to about 50% of the channel that works but the heater voltage is correct.

Any ideas? It seems like a fairly simple circuit but it has me stumped.

 

[paczeltf]

What you wrote is confusing. What do you mean by 50% heating, is that about the heater glow? Did you replace both power tubes? Did you try swapping them?

It is hard to figure out what went wrong without the measured voltages at all reference points.