Amp losing power in Crunch channel only?

[Force235]

My 1996 JTM30 sounds great in the clean channel, but, the boost channel is about half the volume. I'm thinking it is the preamp tubes? What do the experts here think?

 

[fitz]

My 1996 JTM30 sounds great in the clean channel, but, the boost channel is about half the volume. I'm thinking it is the preamp tubes? What do the experts here think?

I had a JTM30 for a while.
At about 1/2 channel volume, the boost channel was quieter than the clean channel...
...until you crank it.
Channel volumes evened out when I put the spurs to it.

If you are saying this is a new issue and the boost channel volume is less than it used to be, then tubes can't be ruled out.
If you have spares, you could try some tube swapping.

I also had issues with loosing sound completely on the boost channel.
Tube rolling didn't help.
Problem seemed to go away when I reflowed all the tubes socket pins on the board.