Tweaker 40 not working

[Plainview]

I have a Tweaker 40 head that stopped working. The power tubs glow. The preamp tubes heat up. It works when I plug into the effects loop return but not when I plug into the front. I replaced the preamp tubes.

Any ideas on what to try next? I've not worked on an amp before but I'm adept with a multimeter.

I tried to write a question on the Egnater service page, but I get an error from the Egnater website when I'm trying to submit the ticket.

Thanks.

 

[panhead]

Tweak it some more