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EL34's in MK-IIIs?
Posted:
Sun Sep 06, 2009 8:52 pmby TerrySmith
How much voltage can a EL34 take? If I don't sell my MK-III's, I may try them with EL34 tubes, but I don't want to burn them out unnecessarily.
The RCA book says 800v on the plates, 425v! on the screens, the screen voltages are what I worry about. Any opinions?
Posted:
Sun Sep 06, 2009 9:35 pmby Ty_Bower
If you can observe the screens (through holes in the plates, or whatever) I'd feel better about it.
I ran a set of cheap ($1 each!) Shuguang 6L6 in my Mk3 for a short while. They seemed to tolerate the abuse just fine. Of course, I turned down the bias to keep the plate dissipation in line with something more appropriate for that kind of tube. 70 milliamps at >500 volts is probably a bit too much for them.
Posted:
Mon Sep 07, 2009 5:36 amby TerrySmith
DURRR! I just remembered the MK-2 has the same trannys and use EL34's, so I may try them.
The only reason I'm asking these questions is I've got quite a few EL34's (mostly Chinese) to burn up and I can't afford $200 for KT88 or 6550 tubes right now.
Posted:
Mon Sep 07, 2009 5:45 amby Ty_Bower
Didn't the Mk2 use a 5U4GB for the rectifier? That would drop the B+ by a couple dozen volts. Though I doubt that really makes a difference in this application...
Posted:
Mon Sep 07, 2009 11:30 amby Sal Brisindi
I was going to mention replace the 5AR4 with a 5R4GA, nice tall tube like a 5U4 but with a 2 amp filament. It will lower your B+ a bit.
I have a ST-70 running 4 Chinese 6L6's and a 5R4GA, a great combination. Sounds real nice.
Sal