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Old 3rd April 2008, 03:15 PM   #1
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Default fixed bias for push pull tube amps

i am designing a power supply for a typical 20watt 6v6 push pull amp for guitar.

with the fixed bias supply how much current roughly should it give?

basically by my understanding it is applying a negative voltage to the grids of the power tubes pushing them into their active region.

now for something in the vicinity of -50v bias supply for a 2 6v6's roughly idling at 15mA this bias supply would barely have to push out a milliamp considering the high impedance of a tube yeah?
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Old 3rd April 2008, 04:21 PM   #2
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Pretty much. From what little I know, essentially no current is drawn from the bias supply.
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Old 3rd April 2008, 04:57 PM   #3
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With the possible exception of times when grid current is drawn all of the current consumed in the bias supply will be in the resistors and pots used to set the bias voltage adjustment range.

Generally I aim for about 20mA capacity in my bias supplies, but there is no firm and fast rule.
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Old 4th April 2008, 03:16 AM   #4
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thanks guys!
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Old 4th April 2008, 03:45 AM   #5
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x2 what Kevin said for bias.

But I'm curious as to how you plan on getting 20W from a pair of 6V6's

Cheers!
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