When you bypass the pre amp, and plug straight into the "Power amp in" socket on your amp (Fender Blues Deville in my case), should you be able to control volume with the "volume" knob when the amp is on clean? If not, what should happen?

Im trying to diagnose a loss of volume/early break up problem with the amp, and after replacing the 12ax7 in V1 and the problem not changing, im a bit lost. Does anyone know how the "power amp in" socket should behave?
All of the controls are preamp controls. "Power amp in" bypasses the controls and takes you directly to the output stage. Plug in a "line level" signal from a preamp, keyboard or mixer to "power amp in" to test your power amp tubes.

Time for fresh tubes?
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
Last edited by Cajundaddy at Mar 4, 2014,
If your amp has global master volume there is a good chance it is after the FX Loop and you can use it to adjust volume. With channel volumes only, nope. They are before FX Loop. You have to adjust the volume with your guitar or the possible pedal/effects unit you have connected into the Power In.

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There isn't.

You've proven that the fault wasn't V1. Don't stop there. Now move onto V2 and try the new tube in there. If that's not it, try the next one, and so on.
If after trying it in every position it is still doing it, it's time to move onto the power tubes. ie replace them.
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