I've had a newly built Dynaco ST-35 for some time now and it's worked really nice, apart from a little hum in the left channel. I was able to squeeze in the Enhanced Fixed Bias as well. Everything is new.
Before I built this unit, I checked all resistors before and after to make sure the values were as advertised. Everything was spot on. I decided to check them the other day, along with voltage readings. Voltage readings were fine with the output tubes, but a little weird with the input tubes. All resistor readings were good except for the 300K (R5) in the left channel. It measured 390K whereas the right channel measured 300K. Not sure how the resistance increased after the amp was put in use, but I'll a get a new one tomorrow.
Voltage readings on the input tubes were (published specs to the right)
L R
PIN 1 - 246 VDC 230 VDC 215-230
PIN 2 - 90 VDC 113 VDC 112
PIN 3 - 113 VDC 128 VDC 116
PIN 4 - 6.0 VAC 6.0 VAC 6.3
PIN 5 - 6.0 VAC 6.0 VAC 6.3
PIN 6 - 96 VDC 115 VDC 112
PIN 7 - 0 0 0
PIN 8 - 0.73 VDC 0.90 VDC 0.85
PIN 9 - same as pins 4&5
The right channel figures are good except for PIN 3 (cathode) which seems too high. Not sure why this is. Any thoughts?
Left channel PIN 3 is very good however, but the other readings may come on with replacing the R5 resistor maybe?
Any insight into this "problem" would be appreciated.