Harmonica Amp

[GusGus]

I got my harmonica valve amp finished. Looking pretty sharp (no alligators were harmed) and working great. It's a clone of a 1966 Gibson Kalamazoo model one. These are the best small harmonica amps ever made but they are difficult to find and expensive - so I made one instead. I altered the circuit a bit to make it safer and better (hopefully). Seems pretty funky so far. Still got the back pieces to make.

[blueglow]

pretty cool. homegrown or commercial?

[Tweed-Bassman]

Nice! Love the look of that alligator-pattern covering. Did you bend the chassis yourself? Looks like a single sheet of aluminum (or what you might call aluminium, I think). Just curious - Will the back cover include metallic shielding (such as metal window screen, adhesive copper foil or aluminum foil)?

[GusGus]

pretty cool. homegrown or commercial?

I started with a really cheap old Marshal amp case that belonged to one of my kids from years ago. I stripped it, then made up an aluminium chassis to fit. I got the Kalamazoo schematic from the web and then designed and built it from parts.

It uses a 6X4, a 12AX7A and a 6BQ5. The speaker is a 10" 8ohm Celestion clone

The schematic is here http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/

[GusGus]

Nice! Love the look of that alligator-pattern covering. Did you bend the chassis yourself? Looks like a single sheet of aluminum (or what you might call aluminium, I think). Just curious - Will the back cover include metallic shielding (such as metal window screen, adhesive copper foil or aluminum foil)?

It doesn't at the moment. Good idea?

[GusGus]

Here is the back finished



I also built an attenuator from plans I found on the net. It gives a great overdriven Chicago blues sound without rattling the windows and making the dogs howl.

[Tweed-Bassman]

Wow! I've never seen a heavy-duty wire-wound potentiometer used in a guitar effects pedal! But if you had it lying around and the value is right, why not?

[Tweed-Bassman]

Nice! Love the look of that alligator-pattern covering. Did you bend the chassis yourself? Looks like a single sheet of aluminum (or what you might call aluminium, I think). Just curious - Will the back cover include metallic shielding (such as metal window screen, adhesive copper foil or aluminum foil)?

It doesn't at the moment. Good idea?

Most of the better guitar amplifiers I've worked on have used some kind of shielding in whatever part of the cabinet forms the final side of the open chassis. For amps like yours, where the open face of the chassis faces out the back side of the cabinet, this shielding is usually installed on the inside of the back cover. Fender used metal window screening in the old days, but has moved to adhesive aluminum foil in more modern designs. If you have adhesive copper foil, that makes an excellent shield! Apply it to the back panel in a way that allows it to touch the edges of the chassis. That way, it forms a complete electrically-conductive (and grounded) Faraday cage. I've even seen "conductive paint" used, but I'm skeptical that it works as well as actual metal for shielding.

[GusGus]

Wow! I've never seen a heavy-duty wire-wound potentiometer used in a guitar effects pedal! But if you had it lying around and the value is right, why not?

It's a rotary L-Pad controller. The design page is here with the explanation of how it works

https://guitar.com/guides/diy-workshop/ ... ttenuator/

[caffeinator]

Hi GusGus,

Excellent work! Your tolex work is impressive! What sort of adhesive did you use?

As for shielding, screen, perforated metal, copper foil, aluminum foil, sheet metal, and shielding paint all work. However, if you're not getting bothersome noise pickup or hum, they may not be necessary.

What mic are you using?