[Amps] Toroidal filament choke and DC current

[Carl]

Pete, the TL-922 has the 3-500Z filaments  in series and the flat ferrite 
flat bar filament choke is quite small and 22uH. but I have no idea of its 
ferrite specs. That amp makes full power on 160 with ease. If you have 
access to a 20 or 40V transformer or a small Variac the wire size drops 
dramatically.

You could then use a pair of  4"  x 1/2" 33 mix rods taped together. The mu 
is 800 and I have plenty on hand at 1990 prices.

Or at 10V use the classic 7.5" x 1/2" rod and #14 wire.

Many amps use the filament choke as part of the L for the 160 or 80 input 
network. The RF only "invades" a part of the choke which is also bypassed at 
the cold end so noRF gets past that point in any case.

Just a couple of ideas.

I have also used ferrite rods with a neutralizing winding added to stabilize 
twitchy Heath and other amps on 10M.

With a good layout and the 813 shells grounded they should be stable on 
10M....at least mine was (-;

Carl


----- Original Message ----- 
From: "Peter Bertini" <radioconnection at gmail.com>
To: <Amps at contesting.com>
Sent: Wednesday, January 03, 2018 2:51 PM
Subject: [Amps] Toroidal filament choke and DC current


> 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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> Amps at contesting.com
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