Hammond Organ amp to guitar amp


2010-12-13 10:19 pm
Hi I have an amp from an old Hammond Organ (L100 I believe)

Someday I'd like to make something along the lines of a Marshall 18W clone.

For now however I'd just like to get it working pretty much as it is.

Any suggestions on where to start would be appreciated.

I haven't built any amps yet however I am an electronic tech, unfortunately tubes were not part of the curriculum when I was in school.

Also about to mod a Blues Jr, Billm mods + a VVR3 when they arrive.

Thanks for any help you can provide.

I think as a first go at it I would...

1. Disconnect the feedback loop (goes through the factory gain adjustment pot).
2. Remove the key click compensation cap (in parallel with the anode resistor of the VAS just before the PI.
3. Inject your signal right after the spring reverb and rewire that first 12AX7 as a simple CC gain stage as in most guitar amps.
4. I would probably put a simple volume pot before that first gain stage just to get it working.

After this you can work at making an actual 18W ish type as everything you need is there IIRC. You could even go with a more complex front end later with TMB stack and extra gain stages.