Gryphon

Havent seen any mention of the 2xxx series JCM900 - the 'high gain master volume' models. These are single channel but have two volume controls that are footswitchable. No reverb is one difference between the 2xxx series and the 4xxx series. The other is the tone - the voicing seems completely different - as previous posts have said, my 2502 combo is like a regular 50w Marshall with a built in OD pedal that you dial in using the 'sensitivity' knob. However, unlike a 4xxx, a 2xxx series doesnt do clean, but everything beyond that is great. I bought mine new in 91 and still have it, and have never gigged with anything else. It produces great rock tone at low (or high) volumes. Viva diodes!!

Other reasons JCM900s get a bad rap in the US are:
1) EL34s were in short supply so a whole bunch were shipped over with 6550s. But of course you can retube and rebias with (Svetlana winged =C=) EL34s to check those out
2) The 2xxx series have no reverb, but all have effects loops so this is easily redressed