Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: Bryce.Y Thanks guys. I'll have a look.B... -- 12/20/2003 2:37 AM View Thread

Re: Bias balance in SLO

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.  
---Wild Bill