Others may have more direct (and successful) experience in this area but here's what I've found; I've got an L122 all tube tonewheel spinet Hammond from 1966 that I've done quite a lot of work on and use quite a bit for noise band recording projects. arcaxis is right about their lack of gain at the front. The Hammond runs up to full volume without much distortion so to me neither the pre amp or the main power amp is running a huge amount of gain. I guess to Laurens Hammond distortion was the great evil and the whole thing was designed not to overload.
If I do want to go into evil distortion, I tap into the rca connection between the pre and power amp and stick a valve distortion pedal in there. Sometimes I slap a little berri mixer in there also if I want to split out a signal and send it to another amp. Then I put the distortion pedal into the mixer's effect loop.
But noise goes up too. And that rca connection is post pre-amp / pre-power amp so the pre-amp gain is still as per the original. I can use the mixer to boost up the pre amp gain and drive the power amp into more distortion as well if I want too.
So, it's the pre-amp gain (or lack of it) that kind of rules it out as a guitar option to me. Also, the pre-amp input is not rca from what I can recall.
The whole thing only runs about 15w push pull I think but it's got a couple of nice old 12" alnico's in it. I think they may be voiced differently from each other, one for a bass response and one for a treble one, or at least all the manuals I've got for it give that impression.
I don't know that I'd bother myself. I think there are much better 15w dedicated guitar amp / speaker options than the Hammond in my view. My little 15w Blues Junior can chew it up as far as a guitar tone and volume goes.
Anyway, I couldn't imagine hacking into the old girl to change her reason for being. They are starting to get rarer and are now going up in value (or were until the botttom fell out of the world). And they're great to work on and to play.
