Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => EZ Board postings => Topic started by: Geezer on June 17, 2005, 08:13:38 pm
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Hoffman Amplifiers
> Tube Amp Building - Tweaks - Repairs
> EL84 bias question
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bluesbear
Hey get your own solder
Posts: 313
(1/30/04 11:28 am)
EL84 bias question
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Hello! I'm working on an amp with EL34's, something I've never done before. No real problem but I don't seem to have any info on safe operating range for the bias current for this tube. If anyone knows of a chart somewhere that lists the power tubes and the bias ranges for them, THIS would be real archive material!
Thanks!
Dave
Tiny Daddy
I will work on all amps
Posts: 459
(1/30/04 11:50 am)
Re: EL84 bias question
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Bias for 70% plate dissipation. Depends on tube current and tube voltage drop with no signal. Some bias their tubes slightly hotter.
Rotting27
Junior tube assistant
Posts: 102
(1/30/04 7:32 pm)
Re:
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Everyone has their own special way of biasing tubes. I use a simple method that has yielded great results, so you can, at least, give it a shot to see if you like it.
bias current = (2 * Power rating of the tube) / (B+ * 3)
So, in your case an EL34 has a power rating of 25W. Let's assume your B+ is 475V.
(2 * 25W) / (475V * 3) =
50W/1425V =
.035A =
35mA
Keep in mind that this is PER TUBE.
Rotting27
Junior tube assistant
Posts: 102
(1/30/04 7:39 pm)
Re:
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Here's a listing of power ratings for popular tubes, for reference and to plug into the above equation.
EL84, 6V6. 6BQ5 = 14W
Chinese 6L6G/GB/GC = 19W
Sovtek 6L6GB, 5881 = 23W
EL34, 6CA7 = 25W
6L6GC = 30W
6550 = 35W
KT88 = 42W
bluesbear
Hey get your own solder
Posts: 316
(1/30/04 7:45 pm)
Re: Re:
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That's exactly what I was looking for. I like to get within a safe range then play around the edges till I'm satisfied. It's best to know how far you can go before you start, thoughj. This'll help!
Thanks!
Dave
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