I'm not sure I understand the problem. Are you having a hum problem, a
feedback problem or a feedback problem that sounds like a hum. Things to
check:
1.If you turn on the amp, and turn up the volume without the guitar plugged
in, is there noise.
2. If you insert a guitar chord and the guitar, with the volume off and then
turn up the amp, is there noise?
3. If you change chords, does the noise change?
4. If you use a very long chord, move the guitar far away from the amp and
keep the volume low on the amp, is there still noise? You may need a second
person-one person to strum the guitar and anothe to listed closely to a low
amp.
5. Does the noise change as you move around--in front of the amp, to the
side of it,
behind it, etc.
6. Is the noise low pitched or high pitched?
To interpet these: If the noise is present without a guitar..the amp has an
issue.
If the noise changes when you switch chords, you may have a fault in a
chord.
If the noise is present with a quiet amp, it is probably not feedback. If
the noise changes as you move around the amp it is likely feedback. If the
noise is steady and
low pitched, it is probably not feedback.
If the hum is approximately a concert Bb (on the A string)it is 60 cycle
hum, if it is approximately a B (open B string) it is 120 cycle hum. These
both derive from 60 cycle
AC power.
So, let us know, is it hum, feedback, or both?
Al