Originally Posted by Jae

Well, for 2203 and 2204s there are many different years for that. I think they started putting in diodes after 1984. Anything past 1984 I think have the diodes. Anything pre don't.

Also I have a JMP Master lead 50W (2204), which is from '78. Not called a JCM800 and cosmetically different but I'm sure it's the exact same circuitry as the JCM800 pre1984. Interesting to look at the history of these.