mark IIb mod questions: simul mod & fx loop mod

[JimAnsell]

ok, so my mark IIb coliseum has "simulmod 4/99" written on the back, and what looks like randall smiths initials.

when looking inside, you can see some glue and different material resistors on the innermost 2 tube sockets.
what does this mod do exactly?
i'm guessing that it makes the inner two tubes run in simulclass.
so can i use el34's in those middle two sockets?


also, as much as i love the amp, the fx loop is pretty shitty.
my boss dd-2's repeats in there are pretty distorted.
i've read that boogie does some fx loop mod to these amps.
what does that do exactly?

 

[JOEY B.]

Looking at your pictures in the other thread, the inner sockets are indeed wired in triode (aka Boogie Class-A). I would not use EL-34's in those sockets until you can ground pin#1 of those sockets. They currently appear to have nothing connected at that position. 6L6's will be fine though.