Hi,
got a question about the calcualtion.
If I use 6L6 they can handle about 30 watts each.
If I divide 30 watts by 480 volts (BF Vibroverb project)
I get 62.5 mA of max current.
If I would bias at around 35 mA (many articles say this is the optimum),
then I am right in the middle and basically in class A.
Is the basic calculation correct?
Is there any information on how a Blackface Fender was supposed to be biased back in the days?
Cheers,
Stephan
Biasing power tubes
Moderators: pompeiisneaks, Colossal
Re: Biasing power tubes
Yes, 35mA equates to 50% plate dissipation, so it's in the middle in that sense.If I would bias at around 35 mA (many articles say this is the optimum), then I am right in the middle and basically in class A.
However, there's no direct correlation between the class of amplifier operation and the plate dissipation of its output tubes.
ie it's not correct to state that a particular plate dissipation will result in class A or class AB operation.
I suggest that unless you particularly want to get deep into the theory of it, don't worry about amplifier class. There are probably some topics more relevant to guitar amps that would yield greater benefit, see http://www.valvewizard.co.uk/
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Stevem
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Re: Biasing power tubes
35 as posted is in the middle and 42 would be as hot as I would go!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Biasing power tubes
Yeah, most people don't use the 70% rule with current production power tubes.
Of course that depends on manufacturer and type of tube but I find, especially with 6L6GC's that I like a colder bias.
Usually around 50-55%.
A colder bias usually results in longer life of the tube.
Also, check the filament voltage to the tubes.
Longevity of tubes is best the closer you are to the design limit of 6.3 vac, for most tubes.
Of course that depends on manufacturer and type of tube but I find, especially with 6L6GC's that I like a colder bias.
Usually around 50-55%.
A colder bias usually results in longer life of the tube.
Also, check the filament voltage to the tubes.
Longevity of tubes is best the closer you are to the design limit of 6.3 vac, for most tubes.
Tom
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Don't let that smoke out!