El34 winged C's running at 45 ma. Issue?

[kingsxman]

I just checked the bias on some Winged C EL34's that a tech installed and supposedly biased in my 1987 JCM 800. Both were running at 45 ma current draw and had a plate voltage of 450 v. (I was using a weber bias kit probe and my multimeter). I had previously installed a set of Groove Tube EL34 (6CA7EGE.. or whatever that GE reissue is) in the amp and biased them at about 38 ma. I had the bias pot all the way down to get there..

I called the tech and said "what up!". He said he usually biases them at 35 ma...so they must have drifted. wha??? 10 ma drift?

Anyway, a little background that my previous tubes blew up after 3 gigs. I've played 3 gigs now with the Svets and figured I was safe. Is this high reading a cause for concern? Could the amp be slowly going and causing the current draw to increase? I'd be more apt to think that if 1 tube was high...but they both are.

comments?

 

[Greggy]

Given your plate voltage and maximum wattage dissipation for el34s at 25 watts, you should bias within the range of 33-39 ma.

 

[kingsxman]

Greggy, I'm guessing that my bias pot is adjusted all the way down. I'm going to check today.

 

[Greggy]

If that's the case, on some amps you can change out the resistior immediately after the bias pot to a different value to increae the range of the pot (forgot if you have to go up or down in value to increase range). Someone here should know.

 

[kingsxman]

Turns out I DID have some wiggle room in my adjustments. I put it at 35 ma draw with no load or signal. Think thats a good number?

 

[Greggy]

Originally posted by Greggy
Given your plate voltage and maximum wattage dissipation for el34s at 25 watts, you should bias within the range of 33-39 ma.

See above.