Anyone put NOS power tubes in a Mark IV?

[shawnqa800720]

I just put a set of NOS RCA 12ax7's in the preamp section of my amp, and now I am looking to put a set of NOS RCA 6L6 Blackplates in my Mark IV, but am mildly concerned with the inability to bias the amp. I talked to a reputable NOS tube dealer (audiotubes.com), and he recommended the RCA's as an equivalent in terms of current/voltage to the Boogie special groove tubes. I have 30 days to return the tubes, so I would like to know if anyone here has had experience with this, and could give some insight, success stories, failure stories......

Also, I only plan to put the NOS tubes in the outer sockets as I only run my amp in Tweed mode, so never use the middle two - anyone know if this would cause an issue?

Thanks in advance,
Shawn

 

[swbo101]

I don't have any insight on those tubes, but just want to say that tweed mode does not select which tubes you are running. What defines which tubes you are running in the Mark IV is the Class A/Simul-Class switch on the back. Class A = Outer Tubes...Simul-Class=Outer + Inner Tubes. Tweed mode is a variac and just reduces the wattage. So as long as you have Class A with tweed you are running just the outer tubes. I'm not sure if you'd run tweed and simul-class together. It doesn't say you can't in the manual. but not sure.

 

[dodger916]

IIRC, the Class A outer sockets are biased hotter. If so, I think you'd be safer running the RCAs in the inner sockets.