Found this :
I have never checked the plate voltage on an 82 or 83 JCM800 2204 but I do own a stock 1984 JCM800 2204 than runs 6550's that I have checked the plate voltage B+ and it is 450DCV at idle and I believe I had the variac to exactly 120ACV when I took the measurements and recorded all the voltages along the B+ rails mapping all of them so had a baseline for later. So all the voltages will be higher along the B+ rail including V1A, V1B, V2A almost 100 DCV higher plate voltages on the 1984 2204 versus my 1972 1987.
My 1979 stock 2203 running 6550's B+ plate voltage was 454DCV with the stock power transformer it could have been a Dagnall or Drake, I think the OPT was a Drake maybe. It was changed out when Scott Splawn rebuilt that amp but I know what the B+ because I did bias my amps back when it was stock.
My 1972 50 watt SLP 1987 with original stock transformers at 120ACV wall voltage is running 399/400DCV B+ plate voltage.
500+ B+ in any amp does not bode well for tube longevity these days with modern tubes especially EL34's. Modern 6500 and KT88's are a little more robust, it's amazing Wizard amps dont' eat JJEL34's more often especially with Friedman going all EH these days.
My 1972 50 watt SLP 1987 with original stock transformers at 120ACV wall voltage is running 399/400DCV B+ plate voltage.
500+ B+ in any amp does not bode well for tube longevity these days with modern tubes especially EL34's. Modern 6500 and KT88's are a little more robust, it's amazing Wizard amps dont' eat JJEL34's more often especially with Friedman going all EH these days.
All my experience between 50 watt and 100 watt Marshall's is even at the same volumes the 100 watter will always punch harder along the entire frequency spectrum... it just does. It's all due to the increase in the transformer mass, more plate laminations and core windings equals more magnetic flux when the voltage signal is inducted to an audio signal... you just can't get away from the physics of it.
Last edited: Nov 21, 2021
