MKIII green stripe tubes - Simul-Class switch MIA

[Zoner]

I have a green stripe MKIII and from what I can tell it operates in Simul- Class mode unless I use the half power option. There is no switch in the usual place on the back, but there is a small sticker that says "Simul-Class" on the rear of the chassis near the power cord. I like the way it sounds with 4 6L6's but seem to recall being advised to use 26L6's and 2 el34's for best performance and tube life. I was having trouble with it sounding kinda "cold" until I popped in a pair of str 430's in the outside spots which seemed to help a bit. Any ideas about what "should" be used for power tube confguration and why there is no Simul-Class switch on mine? It seems to make some tonal differences but is still ungodly loud even at half power. Can I just yank the outside tubes and go half power that way? Thanks. Z

 

[tim6string]

I use all 6L6s in my Mark IV simul-class and when I had my Mark III I ran the same configuration and really liked it. I have toyed around with the idea of trying EL34s, but I have heard people say they didn't like it as much.
But that is all a matter of taste. I think it depends on the sound you are trying to get (style wise)

Mesa ships them with EL34s now I am pretty sure.

It is always possible that you do not have simul-class, I really do not know what the green stripe means (I am now a Mark III illeterate) but Simul-Class was an option on those amps. I would also think that half power would only use 2 of the 4 tubes, but I am guessing so I will quit.

 

[Boogiebabies]

It's a long chassis MK III and Mesa did not want to spring for a new faceplate. The 1/2 power switch on the front shuts off the two inner sockets. The Simul sticker is just proof positive that you have this option. The short chassis had it on the back.

Unless you try EL 34's in the outer sockets yourself, you will never know what you are missing, or not. I prefer the shred from EL 34's. They do not have the high mid sizzle of a 6L6, but they do not have the natural bottom end either. Back in the 80's when the crappy Chinese EL 34's was about all you could get, besides NOS, they would blow like mad. Hence the using of all 6L6's and their recommendation in the manual. Mesa was covering their *** with the tube warranty. The Simul-Class was designed to run class A/B pentode for the center sockets and class A triode in the outer two sockets. It never really mentions the actual design using EL 34's as the OT has the impedence for it. The power amp circuit uses 470 ohm screen grid resistors like a typical 6L6 circuit. I never really understood why.

 

[Marshall_Fascist]

all green stripes are simul class. I know that for sure.


I like combining both el34 and 6l6, so I get the best of both worlds, and not so much worst of both worlds either.