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EL34 plate voltage 600vdc

12/5/2003 9:16 PM
EL34 plate voltage 600vdc
Sovtek Mig 60 lead head w/(2)El34's. Picked up this amp used & works well. Tubes were El34G's & decided to change out due to age (4+ years). Installed electro harmonix EL34's. Measured plate voltage to start bias setup-630vdc at idle. Set bias to give me 17.5 S.D.watts, about 28ma w/plate at 618vdc.  
Is this high plate voltage normal for this amp?
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12/7/2003 12:02 AM

I don't think it's the right voltage but EL34 can handle this voltage, but Ug2 is max 450 volts.
12/7/2003 1:07 AM
Ian Anderson

I've heard people say those Sovtek amps have high B+ once or twice before, so that's probably correct - reciepe for lots of headroom!!!  
... Ian :)
12/8/2003 2:07 PM
Also a recipe for frequent re-tubing. I am sure they are hoping that you buy Sovtek tubes.  
12/8/2003 7:54 PM
D. Hiatt Collins

"I don't think it's the right voltage but EL34 can handle this voltage, but Ug2 is max 450 volts."
I've got one, but I've never looked inside. However, I do have a Mig60 schematic which shows that the PS is two FWB, one "stacked" on top of the other. The plates are fed from the high node, and screens and everything else are fed from the lower node.  
I've heard that Sovtek amps run their tubes at high voltage, so I wouldn't be suprised if the plates on the Mig60 were 600V, and the screens and everything else were run from a 400-450V tap. That would give you high headroom and power while staying within the tube limits.  
I'll have to open it up and see what mine reads.  
12/29/2003 11:53 PM

I have a Mig 50 (Bassman copy) that runs 580 on the plates, runs 5881's that last forever. My Mig 100h runs 5881's @ 470 vdc on the plates.
1/13/2004 12:46 AM
I once built a 50 watt amp using a tranny  
440 volts through a full wave bridge, it  
B+ was 615 VDC. To prolong the tube life  
an reduce glowing, I suggest that you install  
beefy 3000 to 5000 ohm 20 watt power resistors  
on each screen (pin 4). When you amp is maxed  
out, the voltage differance will heat those  
screen resistors easily.

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