[Harp-L] controlling amp feedback

["John Kerkhoven" <solo_danswer@xxxxxxxxxxxx>]

A question for the amp-savy listers.

I just got my first serious amp, a second hand Seymour Duncan 84-40 tube
amp. It's a guitar amp, not a harp amp. I got it at a good price, and at low
volume I can get some very sweet sounds on the distortion channel with
reverb. Tried it loud in a small rehearsal space with drums, bass and guitar
and had to rely on the clean channel as I could not get the volume I wanted
without feedback on the dirty channel.

Tubes: 3 12AX7s. According to http://www.harpamps.com/ampg/ampg4.html this
is probably part of the problem. He says: "The more 12AX7 tubes, the more
preamp stages. This is good for a guitar player, but bad for a harp player.
The feedback demon thrives in the preamp stages of an amp. One or two 12AX7
tubes are enough. Three is the maximum."

The other tubes are 4 EL-84s.

Microphones I use: Madcat Shaker and an old SM58.

I'm just starting to use this amp and I know a lot depends on the room and
where you stand. I have not tried micing the amp yet and may try that in due
course. And I know that too much reverb can bring on the feedback.

I have zero experience with tube amps. Should I swap some or all of the
preamp tubes? Is this safe to do?

Any other ideas?

Thanks,

John
Montreal