What to suspect first
Not all things are equally likely to fail. Experience with tube guitar amps
has shown that failures are most often in the following order of likehood:
- Operator Error - a control or something is set or switched wrong.
- Tubes - the most likely thing to have gone bad on a once-working amp; this is why they're in sockets!
- Power Supply Components - they handle lots of power and get hot
- Resistors and Capacitors - especially electrolytic capacitors
- Mechanical Components
- Tube Sockets
- Switches
- Switches
- Cables, Cords and Jacks
- Internal Wiring
Accordingly, suspect problems in that order. First make sure you
are operating the amp correctly - master volume turned up, cords
plugged in, etc, etc. Then suspect that a tube has failed, and so on.