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RE: LM317 for PP cathode biasing?

Posted by Alex Kitic (A) on February 19, 2015 at 22:53:49

In Reply to: LM317 for PP cathode biasing? posted by DAK on February 19, 2015 at 21:11:18:

It's an easy task, but depending on the goal could lead to different results.

You can use one LM317 to bias both tubes in a PP arrangement, and you can further decide whether to bypass the LM317 or not. This will set max current for the pair, but the tubes still need to be pretty well matched for optimal results.

You can otherwise use one LM317 for each tube in a pair, achieving perfect DC current matching from un-matched tubes, but you have to bypass each LM317 and are going to be limited to class A operation (neither device is going to be able to switch off because of the constant current draw.

If you have experienced improvements in SE amps, the second approach in particular is going to yield important improvements in PP operation, at the "cost" of limitation to class A operation.


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