Whats the deal with EL34 class tubes in the V

[jdgebha]

I tried emailing Mesa but didn’t get a response. Can you run EL34 or KT77’s in full power mode or not? Whats the official word and the technical reasons for yes or no?

 

[Jeronimo]

EL34 has to run in Variac mode. I don't know avout KT77 tubes.
The requirement for Variac was added in later revisions of the manual. You can run at the full 90 Watt.

 

[jb's 52]

"NOTE: When using the BIAS SELECT switch on the Rear Panel to accommodate the use of EL34 Power Tubes, ALWAYS switch to VARIAC
POWER (switch down) on the main Front Panel POWER switch and operate the amplifier in this power mode until swapping back to 6L6 Power
Tubes. This will ensure uninterrupted performance and avoid running the EL34s over their rated safe operating voltage."

I had to check that new manual revision myself. My 2010 manual didn't say to run EL34s in VARIAC.
With that said, I'm guessing it's because full power is over "safe operating voltage" for EL34s. I'm no EE though.

 

[jdgebha]

If it just to save tubes thats one thing. But if its due to potential damage to grid resistors etc that’s another. I never did receive anything back from Mesa support.

 

[mace]

My Mark V ate a quad of EL34’s in a few months. I always used FULL power at that time (before I knew about the VARIAC recommendation). I would think VARIAC just ensures ‘normal’ EL34 tube life, or in other words FULL power shortens EL34 tube life a lot.

 

[allbutromeo]

Yeah, my 2012 didn't have that bit about the Variac so I ended up blowing the tubes and burning up the grid resistors, took about 9 months for it to happen though. There are probably some El34s that can handle higher voltages and be fine, but if I ever switch back to El4l34s I'll just use the Variac.