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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: RE: Thanks... posted by Nunki on September 8, 2014 at 07:39:11:
It is confusing. Two basic power tube bias circuits make use of either cathode bias or fixed bias.Cathode bias amps use a resistor at the tube cathode or filament (direct heated tubes- 2A3, 300B, etc) to place a positive voltage on the cathode. This positive cathode voltage is reflected back to the tube grid as negative bias. This circuit is normally makes use of a fixed value resistor that is not adjustable.
Fixed bias amps use a separate power supply to provide a negative voltage to the power tube grid. The power tube cathode or filament is grounded to the power supply negative. Many fixed bias amps have adjustable bias potentiometer.
Some vintage amps with fixed bias design used a non-adjustable resistor that can be replaced with a potentiometer for adjustable bias.
Edits: 09/08/14
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Follow Ups
- RE: Fixed vs Cathode Bias - sony6060 08:02:17 09/08/14 (0)
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