I have an ST35 board amplifier that I have been listening to for a while. I stored the amp for about 3 months then dusted it off to use again. I put in a set of tubes and fired it up into a load and adjusted the bias on all the tubes to 35mA per tube. I was about to button up the amp and put it into service and realized one of the screens of the power tubes was glowing bright. I shut down the amp, set the bias pots to 400 ohms as per the manual and tried another set of tubes. To my amazement, the same socket as before had a glowing screen on a known good set of tubes. I did some research and found that if you have an ultralinear amp without resistors between the screen and the OPT that there could be arcing events. I installed resistors between all screens and the OPT, still the same socket is has a glowing screen on the tube. I checked the voltages on the pins and nothing looks out of order. Has any one else had this problem? How did you fix it?
Thanks