Dear Chris. Oh Boy! Now this is just what an old timer like myself really
enjoys. I remember well my old push pull TZ-40's with a swinging link tank.
You have asked a chapter full of questions, so lets get started. The coils
that fit with the swinging link are the final tank coils. If they are
numbered, they might indicate 80, 40 etc on them. If not, the one with the
most turns will be the 80 meter coil and so on decreasing the coil turns.
As they decrease in number, they will likely get larger in wire size. 160
meters back then was limited to low power and other restrictions and would
have required additional plate capacitance to be switched into the circuit,
so I feel sure that we can rule out that band. The number of turns on the
swinging link allows you to match the output to the characteristic impedance
of the feedline. The feed system on popular antennas would likely have been
balanced line. These may have consisted of zip cord, twisted cotton
insulated line, twin lead or home made balanced feeders of up to 6 inches
spacing. You can feed coax from a link coupling. More on that another
time. The plates are fed through the center of the tank coil. The variable
capacitor in the tank circuit is your plate tuning control. You control the
plate loading by closing the link into the center of the coil axis. You
must use push pull in the input tuned circuit as well or otherwise you wind
up on DSB ! Don't want that. These coils will likely be smaller in size
and will also have individual units for each band. Most likely here we will
find a fixed link coupling to the exciting stage. You will resonate the
circuit by tuning for maximum grid current in the finals using the input
variable capacitor. You have not told me enough to determine if you need to
limit the drive. This can be done in the grid of the driver tube via a
linear taper pot. I also do not know enough to give you information on
the keying for cw. It should be biased near cutoff to keep the quiescent
current within safe limits. I noticed in your schematic that appearantly
the amp switches between class "C" and "B". He is using the filament
transformer to derive grid bias needed for class "B". The capacitors
between the plate and grid circuits are the neutralizing "condensers".
Neutralization needs to be done before firing up the unit. More to follow
there also. The 250TH use 75 watt filaments. You should expect to see
color in the plates under load. Tell us more so we can enjoy writing more
epistles. Best wishes.....Bob , K4BG, Sylvania, GA
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