Amp bias numbers and the Tube current numbers?

  • Thread starter Thread starter Laars
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Laars

Laars

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I was hoping someone could explain this to me. I've always used Groove Tubes so I never had to deal with this, but I'd like to try different tubes.

If my amp has been biased at 30MA for the tubes that are in it EL34s , does this number need to match the Ma number that we find on the tubes. If you go to the Tube depot they have this listed on there tubes...

B+ voltage is 400 V DC
Plate current is 29.5 (almost 30)
GM 5100

BlackSabletubes.jpg


Is the bias number of my amp (30Ma)the same as the plate current I see on the tubes?

Reason I'm asking is, I bring backup tubes to every gig, and I want to buy tubes that I can drop in if something happens live so I can get through the show.
 
So can you have B+ 420 V DC in the amp, and still get 30ma for a bias? I was under the understanding that if the B+ voltage went up, the Ma would go up with it. It doesn't?

Maybe I'll post this in the Voodoo section and have Trace answer it. Its on one of my Voodoo V-plex amps and on the back he has a sticker that says "amp biased to 30ma".

I just figured since so many of you guys don't use groove tubes, which has the number system, someone must understand how these numbers on the tubes relate to the amps biased numbers.
 
no..it would be different. if yours is at at 420 then those tubes arent a PERFECT match but still pretty darn close. You have about 6 watts of a safe zone.
It is possible that your amp, at 420, is running at 30 ma's right now but you need to either have someone check your bias afterwards or read up , get a meter and do it yourself.

I never trust any co to give me a plug and play tube.
 
So both numbers need to be close then. Thanks for going over this I cant find this info anywhere.

The part that is driving me crazy is, they put those numbers on the tubes, then you look at the spec sheet, and I can't even find them anywhere. So what is the spec sheet for? Shouldn't the spec sheet have a range for the tubes, and then the tubes are a value?

For instance, these are the tubes that are in my amp right now. Svetlana EL34s
http://www.dougstubes.com/el34-svetlana.pdf
 
Hi Jerry,
Thanks for attempting to explain this to me. I have two Voodoo V-plex amps. On the back Trace put a sticker that says "amps bias set at 30mA on 04/09". The tubes in the amp are the Svetlana EL34s.

I wanted to get a set of back up tubes to bring with me to the gigs.

Is the B+ voltage something that is set in the amp and fixed by the manufacture? You then match the tubes to that voltage, along with the plate current?
 
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