Millet Max left channel blown?

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Hello,

I built a millet max ~8years ago, and have put some hours onto it. The other day while listening, one of the channels went out. If I turn up the volume, I hear a crackling of bass notes. No capacitors looked blown. I tried replacing the tubes, and the same problem happened. the headphones work fine plugged into my phone. Does anybody know where to start checking? I was thinking it could be the muting circuit? My source is an old logitech squeezebox touch, and the same issue happened using my phone as a source, so I narrowed it down to the amp itself.

Thanks in advanced!
 
MAXsch75.jpg

this ?
what are the voltages? is there before output cap a 1/2 DC ?
what voltages on anodes ?

i see one trimpot in each channel , seems it is only for bias curent adjustment.
put it too high, and some parts may overheat and fail.
 
Thank you for the responses!

psu: 27.2VDC (within range)
left channel tube: 16.45VDC (supposed to be half psu voltage, 13.6V)
right channel tube: 23.45VDC (supposed to be half psu voltage, 13.6V)
left DB 200mV (should be 66mV - 110mV)
right DB 200mV (should be 66mV - 110mV)

seems like I biased the DB's too high and possibly burned out some parts out prematurely?
 
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