01A question

[mcandmar]

I think i answered my own question, i have been testing the amplifier with RMAA and seeing identical gain and measurements on both channels with the gyrators set to 3ma, and the bias voltages the same. Plates were reading 123v & 116v.

Ale if your reading this i need help, i think i have damaged one of my Gyrator boards.

I had both set to 3ma (measured across the 10ohm resistor R5), i went back to tweak it and one channel read 8ma. Didn't understand why so i quickly wound the adjustment down to 3ma again, and now i am seeing 75v on the plate which makes no sense. Double checked the bias & filament voltages are correct, and tested the tube which is fine.

Any idea what is going on? I suspect i may have damaged the BF862 in J2?

[nashbap]

Originally Posted by euro21

Anode voltage and bias voltage determines operating point (Ua, Ia at -Vg) ... at specified tube and at given condition.

If the tube changing (another tube, or aging), the operating point also changing.

There are no two identical operating point of two tubes, but if it not too far -relative to each other-, it's irrelevant.

The important thing is tubes gain -preferably- similarity at near operating points.

Do you prioritize matching gain over similarity in THD spectra or try to get similar THD spectra and then adjust the gain elsewhere, for example, at the voltage divider just before the SF?
Thanks . nash