Some of those voltage readings seem very high to me. If the measurement is actualy taken across a 1 Ohm resistor, then the idle current through the output tubes in the DSL201 is 675 milli-amps, and the DSL401 is passing almost 1.4 [u]Amps[/u], even before any signal is applied! :eek:

For the sake of comparison, I bias the 7027A's in the output sections of my Ampegs at 35 to 40 ma per tube, measured at the Anode. Measurements taken at the Cathode-Ground connection will also include the bias currents from the grids, but these are typically less than 1 ma each.

If the DSL201 and DSL401 use Cathode self-bias, then the resistor would be much higher than 1 Ohm, and this would account for the higher voltage readings. But there's no mention of that in the service bulletin!

I may be over-reacting here, but setting the bias incorrectly can trash an amp very quickly.