So a friend brought me two amps to fix today. One, a Mesa Dual Rectifier, turned out to need two new preamp tubes and a new input jack. And after that, I must admit, it sounds positively beastly. WAY better than the Triple Rectos I used to own. If they'd sounded that good I'd have kept them. But the other amp is a DSL100. And it appears to be stuck in mute. OT meters out 36 ohms to ground on one leg, 30 ohms to ground on the other leg, on the input (tube) side. Output side meters out at just a couple ohms on any tap. Seems OK. Screen, plate, and bias voltages are in typical ranges. All the tubes test OK. There's just no audio. Fuses are fine. If I could find the proper schematic for this amp I'd have it solved in minutes. Signal path tracing will reveal the problem.