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If you have a pair of 300b's that test in the "middle" between good and bad and have an amp that you can adjust the bias for say, 60 mA, and it holds steady for days/weeks...would I be getting about the same sound as a like tube that tested very good into the green?
How about in another amp where you can't adjust the bias? More likely to sound less dynamic in this type of amp?
Follow Ups:
Direct filament power triodes are tricky to test due to the filament voltage sensitivity. I would believe the subject tubes are good and will sound good.
Are they better off when I can set the bias myself as opposed to a plug and play SET?
I prefer adjustable fixed bias amps.
?? fixed but adjustable? how does this work?
N.
The times, they are changing...
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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