I'm building a four tube 813 amplifier and I am planning to use a 240-43
toroid core for the filament choke.
I've seen some concerns about core saturation due to the DC cathode current
involved in this application.
I was planning to add a third winding (trifiliar) to allow bringing the
filament transformer CT back to the top of the windings, thus cancelling
the DC field. I'd have to add a second ferrite rod choke to fully decouple
the third winding, but it would be a trivial task.
I was also going use the core to provide a bifiliar winding for
neutralization, if needed. All windings are 7 turns, which yield about 50
uH and over 500 ohms Z at 160 meters. Core is wound and ready to go.
Any advice, encouragement, or warnings?
Pete k1zjh
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