Well, the JCM900s are blamed for their diodes in the pre-amp. Total rubbish, they can sound great. The problem is only in peoples heads: If-its-not-all-tube-it-cant-be-good. Bla bla.
However, the 900s are a very nice thing as "tuning objects". A skilled amp tech dude can tweak them to *really* good sounds. I once had one, but sold it. Today I use a (tuned) 6100LM for guitar playing. Best heads Marshall ever made
MHB 3039 -- After listening for over 30 years, searching and waiting for alternatives, I understood that there will be no other band like Motörhead. Never.