Hi all I have a 100 watt JCM 900 Dual Reverb head with a serious bias issue. Power tubes (6L6s) in V1 and V2 were red plating. Done all the usual tube swaps to rule them out. I took a measurement on pin 5 of each socket with the tubes removed. Valves 3 and 4 were a perfect -30 and -50 with the bias turned to either extreme. Valves 1 and 2 were unreadable. The multi meter would not keep still long enough to take any sort of reading. Furthermore, when I turned the power off after each reading the meter steadily droped to zero on 3 and 4 but kept going mental on 1 and 2 for a long time after the IEC had been pulled. Just to clarify....by 'valve 1' I'm referring to the one closest to the pre amp valves with 2, 3 and 4 following in a line. Ideas??