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Put a capacitor in backwards and it fixes the problem???!!!

Time to 'reassemble' it. Clean up any rework you are not happy with, confirm nothing is going to short and reattach the board to the chassis,

Leave VR606 fully CCW for now. Turn it on and allow it to warm up until is seems to be stabilized. Measure the following, black meter lead on chassis ground:

*Left* channel idle bias, voltage at R525 (TR508 emitter, meter on 200 mV range) -
*Right* channel idle bias, voltage at R625 (TR608 emitter, meter on 200 mV range) -

*Left* channel centering, voltage at TR508 collector (meter on 20 volt range) -
*Right* channel centering, voltage at TR608 collector (meter on 20 volt range) -
 
508 emitter 19.1
608 emitter 2.1

508 collector 11.89
608 collector 13.92

On a side note, tried music and it sounds really good!
 
rudkinst said:
508 collector 11.89
608 collector 13.92
Click to expand...
Let's touch these up first, as they have a secondary effect on the bias current.
Measure the voltage on the collector of TR608. Adjust VR605 for a voltage of between 14.0 and 15.0 volts (shoot for 14.5V).
Measure the voltage on the collector of TR508. Adjust VR505 for a voltage of between 14.0 and 15.0 volts (shoot for 14.5 V).

rudkinst said:
508 emitter 19.1
608 emitter 2.1
Click to expand...
The manual recommends these pots (VR506 & VR606) be adjusted for 10 mV. (Or minimum distortion if you have a distortion meter.)
Start with your new additions and while monitoring the voltage on the emitter of TR608, adjust VR606 *slowly* CW. You are shooting for 10 mV. Allow it to stabilize a bit after each pot adjustment. You will find that adjusting the pot at the low end will have only a small effect on the voltage, but as the pot gets closer to it's CW end, things get a bit more touchy. You are shooting for 10 mV, but in real life (unless you have golden ears) anything between 5 mV and 15 mV is OK.

Now on the left channel, 19.2 mV is a bit high. Monitor the voltage on the emitter of TR508 and adjust VR506 to bring that down closer to 10 mV. Again, 5 mV to 15 mV is OK.

As they interact a bit, repeat the above adjustments (centering and bias) until you are happy with the results.

rudkinst said:
On a side note, tried music and it sounds really good!
Click to expand...
That's good to hear. You never know if you have been working the real root cause until the final test.
 
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VR506 was the touchiest but got it to 10.9. the others are almost exact.

Stereo makes almost no noise when it shuts down, also.
 
rudkinst said:
VR506 was the touchiest but got it to 10.9. the others are almost exact.
Click to expand...
Good.
Yeah, that circuit configuration is touchy. That resistor we added in parallel with VR606 helps bring the adjustment down into the lower end of the range where it is not as touchy.

If you are happy with it, put the covers on and enjoy!
 
Ylli said:
Good.
Yeah, that circuit configuration is touchy. That resistor we added in parallel with VR606 helps bring the adjustment down into the lower end of the range where it is not as touchy.

If you are happy with it, put the covers on and enjoy!
Click to expand...

I am, and thanks again!
 
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