Tube Amps / Music Electronics
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|previous: Bryce.Y Thanks guys. I'll have a look.||View Thread|
|12/20/2003 8:17 PM|
|Wild Bill||Re: Bias balance in SLO|
One old trick that I like is to take a pot somewhere between 100R and 250R, tie the wiper to ground and each outside tap to a cathode. The regular cathode ground path is removed so the idle current must flow through the pot to ground.
You must use a "real" pot, something 2 watt rated. Any old hum balancing pot scrounged from an old amp is probably ok.
The idea is that you now have a small cathode resistor shared by each tube that you can swing in value from one cathode to the other. In effect you are adding or subtracting just a little cathode bias to each tube to compensate for one tube being hotter than the other.
I like to use a 1R resistor to connect the pot to each cathode. This gives me a convenient test point to double check the idle current to each tube.