12bz7 preamp sub for 12ax7?

79 Transam · Post by **79 Transam** » Wed Nov 09, 2005 10:59 pm

I just came upon a couple 12bz7 nos from tung-sol.
Has any one used these in a Marshall?
I have read that they can be substituted for 12ax7s

dynaman · Post by **dynaman** » Fri Nov 11, 2005 6:34 pm

I tried them in a Marshall before. They stunk. They made a bad humming noise. I tried multiple 12bz7's and they did the same. The amp would play but the noise was unbearable. I tried them because I saw them being advertised as a hot rod high gain replacement for the 12ax7.

Go ahead and try them, I'm curious to see if anyone else has the same problem.