Had one se tot tubes in the amp, a set of SED Winged-C 6L6's. Biasing a Bassman RI LTD, that has an adjustable bias pot. With the Winged-C's I could get the bias to something like 22mA with the pot max'd out. With the TAD 6L6's I was able to get the bias to 37mA. Measured the plate voltage off of pin 3 at 440volts. Used a plate dissipation of 25 watts for the TAD 6L6GC tubes I'm using. (25w / 440v) x 0.7 + 0.397, or 39.7mA, but the highest I could get the bias before maxing out the bias pot was 37mA. So why can I bias the amp hotter with one set of tubes over another?