Designing a high voltage tube overdrive for an old Hammond organ.

[HeavyFog]

Hello everyone! I've bought myself an old Hammond T-262 tonewheel organ. The circuitry is solid state instead of tube but it still has a really nice sound, only problem is that it doesn't distort at all with the built in speakers. This is by design, so to get more dirt i plan on running an attenuated line out from the power amp so i can run it through pedals (including a rotary sim) and then into my guitar amp. I figured a great way to get some dirt would be to build a high voltage tube preamp that i can run before the leslie sim to get the dirt i want.

Anyone have any recommendations on where to start with a schematic? I was thinking something along the lines of a marshall style preamp but i'm not entirely sure. I'd like to do start with a 2 dual triodes and work from there. If anyone has any ideas i'd love to hear them!

[anotherjim]

You might look at Alembic F2-B clones. It really only needs 1 dual triode tube and there is a design on the web that shows how to use a pair of small low voltage transformers to power the heater and the HT without getting an expensive tube amp transformer. The Alembic design is actually a clone of a Fender amp input, complete with TBM tone stack, you can probably delete the tone controls except for a 0.1uF coupling cap.
http://moosapotamus.net/ideas/alembic-f-2b-preamp/


If it's Jon Lord distortion you want, then you may want to clone a JTM45 preamp.

[HeavyFog]

The alembic f2b seems like it could be a good choice but i dont think it has enough gain, so a JTM 45 or SLP preamp might do the trick. I got some very good results with a big muff before the leslie sim, so i don't think a fender preamp will quite cut it.

Keith emerson used to use Hiwatt amps to push his leslies so perhaps a hiwatt preamp might be a good choice to bring out the key click a bit more?

[anotherjim]

Apart from hi-gain varieties and different tonestacks, there are really only subtle differences in most tube pre-amp stages. Some may include a cathode follower to drive the tonestack, but that doesn't add gain or distort much.
Without a tonestack, the F2-B has a hell of a lot of gain and the output will need attenuation. Actually, to suit most modern inputs, it needs attenuating anyway.

[PRR]

High voltage is not needed for "dirt". (Actually simpler with low voltage.)

Why not a FuzzFace?

Why not mod the organ's gain-chain? Make R853 R856 smaller; tack 220r across each as a trial.

[HeavyFog]

I've tried a fuzz face and i did like the sound, but i want to do a tube overdrive not out of necessity but because i think it would be a bit of fun. Id like to try something new.

I think a plexi or hiwatt preamp is the way to go.

[amptramp]

A tube overdrive has a great advantage over a transistor design - its performance does not vary with temperature.  And if you follow the Alembic design posted above, you don't need 300 volts for the B+ supply.  In fact, the lower it goes, the more distortion you get until you are down in the low double digits and it dies out.