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Author Topic: FILAMENT CHOKE CONSTRUCTION  (Read 4135 times)
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KD6VXI
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« Reply #25 on: August 26, 2023, 08:03:08 AM »

Henry used those on monoband amplifiers, usually at 13.5 or 27.12 mhz.

Those are somewhat tuned.  No Bueno for multiband.  Problem becomes interwinding C causing resonances as you go up in frequency. Because one winding is inside the other, you can't bandswitch it. (it would be more like bandpass, but I digress).

Chuck Asamoto did a lot of cool stuff at Henry......  But he also has put out a ton of questionable amplifiers (like pallets full shipped to the middle east, that didn't work on arrival.  Uncle Sam was ZERO too happy about that).

Those fils chokes work great over a limited bandwidth.  Then they either don't have enough inductance or they have a series resonance.

--Shane
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« Reply #26 on: August 29, 2023, 08:24:45 PM »

That's why stuff ferrite in for broadband.  There's also one around here somewhere with taps for several bands on the outer conductor, picked up at a fest. Never have needed it but might be interesting to try out.
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« Reply #27 on: August 30, 2023, 05:54:42 AM »

It's a dual solenoid inductor.  Balanced feed for filament.

How does bandswitching half of it work?

Like I said.  Asamoto was pretty smart.

He also did some really FUBAR stud at both ASI and some of the Henry stuff.

--Shane
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« Reply #28 on: August 30, 2023, 01:26:04 PM »

  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
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« Reply #29 on: September 02, 2023, 03:50:55 AM »

It's a dual solenoid inductor.  Balanced feed for filament.

How does bandswitching half of it work?

Like I said.  Asamoto was pretty smart.

He also did some really FUBAR stud at both ASI and some of the Henry stuff.

--Shane
WP2ASS / ex KD6VXI

The taps for bandswitching are on the outer conductor, like they would be on a normal type of copper tubing plate coil. I would presume a cap to ground from the chosen tap or a pi setup of some sort but I'm not qualified to make that guess.
The center conductor just goes its merry way all the way through unmolested. Can't say how well or badly it may work.
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