Good Harp Amp?

[David Root]

For titanicslim, I used Allen Amps iron, I think the TP40D for the PT and the TO40 MT for the OT. Just squeezed them onto a Weber 5E7 chassis. Sorry I've been real busy and out of town for about 3 months now and have not been following this forum as much as I usually do.

As to other mods, I think I mentioned the main ones already. I upped all the coupling caps too. Having some power supply hookup problems owing to my miswiring out of sequence, plus the DC heater supply is out of balance so I temporarily cut it out of circuit and am using standard AC supply. I need to spend a couple of solid days on it because I have two other designs in the pipeline that need to get built too!

[titanicslim]

Just finishing up a modified 5E7 tweed Bandmaster, with cathode bias pretty much to Class A. V1 & V3 are 12AY7s, 150V B+, V4 12AX7 (PI), 330V B+, pair of KT66s about 350V plate. Rectifier (V7) is a 5U4GB Oversized iron for cleaner bass and more of it. Kept the cathodyne PI. Hope to get about 25W out of it. V1-V4, V7 are all NOS.

I replaced the Normal channel with the Mic input from a Gibson GA40, so I can have Fendery triode tone and also greasy Gibson 5879 pentode tone. V3. Separate inputs, not footswitched.

Cabinet is the 5E7 cab but depth is an inch or so deeper for a bit better bass.

Two Weber 10A125 w/Alnico plug magnets, one Weber 10F125 ceramic magnet, each 12 ohms in parallel for 4 ohms. Some builders believe harp amp speakers need to be in parallel, not series-parallel.

I will probably have to tweak the bypass and coupling caps, and the treble tone circuit, but they are all quite a bit bigger than for guitar. PI coupling caps are 0.22 uF, for example.

I did a lot of research on the web. there are several good harp amp forums out there. Bruce at Mission Amps in Denver is a real guru harp amp designer and builder.

Haven't cranked it up yet, but that is coming.

David

Make sure you let us know when that amp is playing.

Dave