The choke cofiguration I used when I was at Drake in 1995 when I
did the new L85 single tube 3-500Z ( now cancelled ) is as follows
(1) 1" dia x 6" ceramic steatite form unglazed
(2) wound with #22 nypol magnet wire for a total of 110 turns. There was a
split silver plated slip ring in the middle of the choke at 55 turns,so
essentially I had two 55 turn windings on the form connected in series. The
ring was used for a soldering point.
(3) Soldered a 50pf 10Kv disc, HT57 or equivalent capacitor between the
TOP(tube connection) and the middle of the winding. This cap must be of
high quality and capable of high currents and dissapation capability. The
disc cap was 1" dia and 3/8" thick with leads mounted at 180 degrees
apart.( This was a custom made unit )
(4) This placed the resonance of the choke at 5.5Mhz (gap between 4-7Mhz)
(5) Coated the choke with dielectric varnish etc
(6) In line choke for 160 meters in series with the plate choke, 1/2" dia x
2 1/2" long with 30 turns for the first layer and another 30 turns for the
second layer wound on top in the reverse direction.
We did not try this at power levels more than 1000watts , but
worked very well for all the bands from 1.8 to 29.7 Mhz for a single 3-500Z
running at 3400vdc. This was exhaustively tested with the usual 3 100? 3
watt metal film resistors wound with 4 turns #16 tinplated buss wire for
the vhf suppressor. We also used 4 different new tubes with the same
results.
Regards Paul
Bramco Palstar Inc.
Piqua, OH 45356
palstar@erinet.com
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