Lots of information here:http://www.captain-foldback.com/Hammond ... matics.htm
I have a 50's C3 and love it, and have also gotten a few salvaged M2 amps and turned them into guitar screamers. Just about all those old time organ amps had extremely good iron and ran very conservitively. Many 50+ year old electronic organs are still fired up on Sundays, and whenever they have choir practice. Not to mention the B3's still found in major recording studios because nothing else sounds the same.