Hi Nigel, Thank you for the advice. Excuse my ignorance, my text books referred as Vbe being "Voltage between base and emitter" will you please draw your suggestion on this? View attachment 63313
That's not the same circuit as in post #17, which I was referring to. The #17 circuit uses a Vbe multiplier, the circuit you posted uses a crappy special diode (D3)
, and is EXTREMELY dependent on the exact components being fitted supplied from Pioneer.
I would suggest making sure R59 is shorted out, and also try shorting out R61 - this will reduce the bias to the minimum possible with D3 fitted.
Personally I'd throw out D3 and fit a Vbe multiplier (with a preset resistor for setting it), then you can set it for whatever transistors you fit.
I would then like to add, when I had the non-original transistors installed, it worked fine for about five minutes. Could the fact that I did not put in new thermal grease be the cause it went into thermal runaway so quickly at low output? I just bought a new tube, since my daughter thought mine would look great in the carpets...
No, it failed because the bias was too high - thermal runaway occurs VERY quickly.