Back to the top of the Amp Debugging Page Back to the GEO Home Page

If it squeals, it's oscillating at a frequency low enough to hear. The single most common cause of this is a tube going microphonic. Try swapping tubes first; it's most often the first preamp tube if it actually squeals solidly instead of only when you hit a note that excites the resonance.

In most other cases, the squeal starts just after some pivotal event - the amp has just been repaired or modified, or new tubes put in, or has been dropped. That event is a clue. Think about what changed, then un-change it or tinker with whatever was changed.