Okay I’m away from home but a conundrum kind of struck me on vacation and I’m trying to wrap my head around this for when I get home. 1961 Fender Super 6G4-A - bias cap has been replaced. Original diode. Filter caps replaced. Original Yellow Astron caps in phase inverter section (I suspect this my be issue) - but let’s leave these facts out of equation for the moment. My experience has always been - if the bias is increased, the plate voltage decreases. Leaving bias resistor the same and not “adjusting” bias, I swapped in three matched NOS Tung Sol 5881 tube sets when I got the amp. Basic Results: Tube Set 1 - 20ma / 450 volts Tube Set 2 - 30ma / 460 volts Tube Set 3 - 35ma / 470 volts Tube bias is stable and I have not checked the Astrons for leakage as the amp was serviced 2 years ago with what seems like a competent tech so I didn’t second guess him as he replaced anything bad. So my question is - if I put in a tube Set that drew more bias current, why is my plate voltage going up. My experience has always been opposite but mostly my experience has been with cathode biased amps. My inclination is as bias current is increasing I’m getting more DC leakage. Lastly I don’t recall the negative bias results but I recall they changed as I expected them to (ie, -ma with every tube swap). But I just don’t have those numbers committed to memory. My intention of course is to get a realistic voltage of 450v or so, and have my nice vintage tubes biased at 50-60%. My memory already isn’t what it used to be - I find I have to learn the same lessons over and over again if not confronted with them regularly. My impression was that something didn’t seem quite right here. Thanks for replies.