If the speakers have only a modest hiss or hum coming from them, that indicates that the power
amplifier section, speakers and speaker wires are OK, and that the fault is probably in the lower-signal
sections of the amplifier.
- Preamp tubes bad
- Preamp power bad
- Input cord or connector is open or has dirty contacts; this can include the effects loop
jacks, if present.
- Input jack dirty or corroded
- Open volume or tone control
- Open, shorted, or failing resistor or coupling capacitor
- Faulty signal wiring
- Dirty tricks - I actually saw this once. The clever-but-misguided spouse of a guitar
buddy painted the tip of a friend's guitar cords with clear nail polish. All of them. That took
a while to find...