My just-finished Express has a problem with hum that I can't seem to figure out. The amp works well and sounds great with the volume set at 9 o'clock, but anything beyond 12 o'clock induces hum.
Symptoms: When I turn the volume up to 12 o'clock or beyond, the hum starts slowly and builds, so it seems to be some sort of feedback or self-oscillation. Hum is produced with or without a guitar plugged in. The chassis is sensitive to vibration, particularly around the Volume pot. I can tap the Volume knob and hear a "thump" though the speakers. Sometimes, if the hum does not start by itself, I can induce it by tapping the Volume knob (or by playing a few notes on the guitar). The hum is not affected by the Presence control or any of the tone stack controls. The hum can be stopped by turning the Volume below to 9 o'clock.
Build: Pretty much a straight forward clone of Francesca. I used KF style gounding, layout, and lead dress. I did modify the heater wires slightly and I haven't yet installed the flyback protection diodes on the power tubes. Pictures below.
New Express Completed - Problem with Hum
Moderators: pompeiisneaks, Colossal