Seems pretty much the consensus, so I'll run with it. I've talked to Frank, WA1GFZ, and he says the same thing. It still puzzles me a bit, though: the equal currents thing...I'd hate to have the ghost of Mr. Kirchhoff rattling its chains in my hallways over my presumption that equal currents don't flow into and out of a circuit element. And in audio applications, like a pair of 811's, for example, you've got 4 amps of 60hz AC flowing through the filaments of each tube—directly heated cathodes—and yet that 60hz hum doesn't find its way into the audio. Not disagreeing with the established wisdom at all; just scratching my head, which is probably why I don't have much hair up there.
In any event, I'll be winding myself a couple of bifilars for my 2X 4CX400 amp (
http://amfone.net/Amforum/index.php?topic=48198.0 ). My original thought was to use 6 amp axial lead RF chokes, because they're small and it's easy to keep the leads short, but I'll stick with the conventional wisdom. Just waiting on a couple of ferrite rods to show up.
A bifiliar choke, on a filament tube, prevents hum.
You really need a teifiliar on things like 8877s, gs35b tubes, etc. The cathode style tubes.
You want currents balanced. Individual chokes don't do that.
That said, they have been used. Then people wonder why they have complaints of hum on their signal, etc.
Then they buy or wind a proper choke.
--Shane
WP2ASS / ex KD6VXI
