Mesa Mark III triode/pentode question

[AtomicMassUnit]

I have the last revision Mark III, and it is the only one with the outer tube sockets wired in normal pentode, where the others were all triode. The schematic shows the older version of the amp with pins 3 and 4 simply connected. Can I safely do this to mine? To get triode operation, will I just connect pins 3 and 4 of the EL34s? The reason I ask is because I have another mark III here on the bench that is wired triode already, and pins 3 & 4 are connected, but they also have some kind of huge diode (it says 8627 610v on it) going from there to ground. I just didn't know if I had to have this or not.

[Amp Kat]

What I think your dealing with is an early Mark IV version. The output transformers are different and they run an Ultra-Linear tap. There is also a current limiting screen resistor on there around 2.?k. The Triode and Pentode modes receive different B+ nodes and the 6L6's have 470 ohm screeners. When you switch modes your also changing taps on the OT. I'm not sure what effect on the transformer it would have shorting the outter and Ultra-Linear tap would have but not sure I'd risk it without finding out for sure from some other more qualified tranny guys than I. Just my .002