Date: Thu, 6 Apr 2023 16:49:57 -0500
From: Mahlon Haunschild <k4oq.radio@gmail.com>
To: "jim.thom jim.thom@telus.net" <jim.thom@telus.net>
Cc: amps@contesting.com
Subject: Re: [Amps] Adding 160 Meters to Swan Mark 1
<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
Henry did all sorts of silly things over the years. That..'tuned input' in
the 8 K ultra has to be one of the dumbest engineering feats.
Wiring cathodes in series is yet another dog's breakfast. The only thing
it buys u is the bifilar fil choke only has to be rated for 1/2 normal
current. Ok, now you have to use a 3rd winding for the cathode return.
The input Z is the same,whether the cathodes are in series..or parallel.
Floating the grids with caps and using a grid choke for the grid current DC
return is yet another fubar mess. Look at the 2k4A. No less than 22
components hanging off the grid pins of a 2 x 3-500Z amp.which is part of
their (non standard) grid current metering scheme..
For a bifilar, 9 uh is ample for a 80-10m amp with a 50 ohm input..and 18
uh is ample for a 160-10m amp, with a 50 ohm input Z..(per winding). Tl-922
also has the cathodes in series,..and used 22 uh pr winding for the
bifilar..and a whopping 80 uh for the 3rd coil. You sure as heck don't
require 50 uh, or 80 / 100 uh for that 3rd winding. That 3rd winding is
just to keep drive RF out of the metering circuit.
The 11m ops will float the entire fil xfmr from the chassis, and use a tiny
bifilar choke in the 240 vac primary to the fil xfmr. They don't even use
a small choke in the CT of the fil xfmr sec. Instead they rely on the uh
between the CT and each outer end of the sec.
Jim VE7RF
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