[Amps] Adding 160 Meters to Swan Mark 1

[Mahlon Haunschild]

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 at telus.net <jim.thom at telus.net> wrote:
> 
> Date: Wed, 5 Apr 2023 19:05:18 +0000 (UTC)
> From: Bill Smith <ko4nrbs at yahoo.com>
> To: "amps at contesting.com" <amps at 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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