This poor Amplifier gave itself a hard time..
Too many components faulty. Mainly electrolytics.
The main resistor supplying the BIAS voltage to the Output Tubes (6L6GC)
changed value under load conditions.
It was replaced with a Bourns 20 turn potentiometer.
The 6.3V AC from the mains transformer burnt out (don't ask...)
and a standby transformer was used to drive the filaments of the phase inverter and output tubes during these tests.
The Amplifier has now been in full operation for > 4 hours. There is hope.
Most of the electrolytics have been replaced. Some resistors burnt out and was replaced.
Added a Bourns 20 turn POT for R108 (5.76K)
That allows for the adjustment of the voltage drop across the resistor (current) that
That allows for the adjustment of the voltage drop across the resistor (current) that
supplies the BIAS voltage.
Glued the Bourns Pot with Pratley Clear quickset.|
(Tested before it got dry. NO conductivity.)
Glued the Bourns Pot with Pratley Clear quickset.|
(Tested before it got dry. NO conductivity.)
Adding another transformer (6.3V~ 20VA), to supply power to the relevant tubes should do the job.
Some pics of the inside...
