The Henry 2K-4 (I owned one of these beasts at one time) was a similar
configuration and used a 50uH 2A choke for the cathode return. The 2K-4 did
not, however, have 160m. Using Henry’s design approach a 100uH choke would be
appropriate.
Best regards
Mahlon - K4OQ
> On Apr 6, 2023, at 1:44 PM, jim.thom jim.thom@telus.net <jim.thom@telus.net>
> wrote:
>
> Date: Wed, 5 Apr 2023 19:05:18 +0000 (UTC)
> From: Bill Smith <ko4nrbs@yahoo.com>
> To: "amps@contesting.com" <amps@contesting.com>
> Subject: [Amps] Adding 160 Meters to Swan Mark 1
>
>
> <In the process of adding 160 meters to my Swan Mark 1 linear I found that
> the <replacement filament choke I purchased from MFJ doesn't have the third
> winding <on it like the original.? ?Looking at the Swan's schematic the
> third winding is <connected to the filament transformer center tap and the
> other end of it is <connected in the center of the tube's filaments and the
> RF Input.? The filament <choke I purchased from MFJ is Part
> Number?10-15115-1.
> <How should I go about resolving this?
> <Thank you,Bill KO4NR
>
> Just looked at the schematic. The cathodes are in SERIES..and run on 10 vac
> ( Same as the Kenwood TL-922). The problem is with the series config, you
> now require a 3rd choke, to pass the cathode current ( sum of plate + grid
> current) back to the junction of the series cathodes.
>
> The TL-922 used a small, 80 uh choke, wound with real small ga magnet
> wire. The TL-922 does has 160m.
>
> You should not require anywhere near 80 uh for this application. 18uh and
> higher, is more than ample. Kenwood used 22 uh for each winding of the
> fil choke. Heath used 9 uh for each winding in the SB-220.
>
> 9 uh = 197 ohms of XL @ 3.5 mhz.
> 18 uh = 203 ohms of XL @ 1.8 mhz.
> 22 uh = 248 ohms of XL @ 1.8 mhz.
>
> Rule of thumb is you want the XL to be 4 X the input Z of the amp.
> IMO, 80uh is gross overkill for the 3rd choke.
>
> Jim VE7RF
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