Well, a long time passed and I have a few of these amps running, but every now and then I come across one which gives me problems adjusting the bias of T1.
Right now I have one amp partially built, basically only T1 with its biasing circuit, and I cannot get the voltage at the base adjusted, with P1, to get a clean output at the collector of T1, it is clipping badly even with a -20dB input sine wave.
The voltage at the base is in excess of 40 volt with a supply voltage of 68 volts, and whenever I adjust P1 the base voltage slowly drifts back to the 40+ voltage.
Why??
Uwe