W2ZM -
Bob
Penn Yan, NY
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Out-of-State AM Page
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2ZM
shown operating his 1KW 1921 rotary spark set. |
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This
is a running 160 meter, 1929 phone rig I use regularly on "top" band. A
UV204A in a Hartley circuit, Heising modulated with a UV 849. Single
button WE carbon mic with cascaded 227's in the speech amp. |
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Three
75-watt lamps are lit up brightly with 2KV DC and it will make 60%
modulation. |
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Shot
of my 1929 Pilot Super Wasp RX. |
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Some
of the West Coast old timers might recall Frank C. Jones of Berkeley
and the "Radio" magazines and Handbooks of the 30's. This is a 100TH KW
set built by Frank that he sold to a man in Binghamton, NY. It now
resides here in my garage. |
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Frank
built it, as he would do with many different transmitters, and did up
the article and then sold the transmitter once the article was prepared
and published. This KW set appears in January, 1938 "Radio". |
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Modulator
deck. Partial illumination provided by energized incandescent
dummy load at upper right. |
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This
is a circa 1970 Continental that uses "four" 4-400A's in parallel in
the PA. They were originally screen modulated, of all things, but a ham
in Maine added a pair of 833's in front of the row of 4-400's and I
finished it up and have it on 160 thru 40 out in my garage. A Viking 2
for audio and RF excitation and 10 KW early RCA mod iron and reactor
[BTA 10F] reside in the roomy cabinet, along with plate iron and filter
choke out of a McMartin 3KW FM set. |
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Some
shots of the Continental 314R1. Shown operating at 1KW output. I have
the blower and fan operating at 120 V and is very quiet yet still
plenty of air to even "kick" the air switch on with no hesitation. |
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The
314R1 uses a pulse-duration modulator (PDM) in the form of a single
3-500Z. The RF finals are a pair of 3-500's. |
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The
Shot of the RF output network, modulator tube (r) and one of the
finals. Plates of finals are at ground potential with modulated B-
applied to cathodes (and grids). Rig has been retuned to 160
meters. |
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The
large pi-wound inductors at right are part of the 5th-order Cauer
low-pass filter used to eliminate the 70kHz switching ripple from
the modulated B-. |
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No
mod iron here! Just a large -8.6 kV power supply and a rather
interesting HV-insulated isolation transformer (left). PDM
waveform is sent to HV modulator through a fiber-optic cable. |
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"Big
Mac", the Mc Martin BA2.5K. It runs two 4-1000's in the final,
modulated by the same. I use a 20-inch box fan mounted on the
rear door for cooling air to the pressurized lower section of the set.
The big squirrel cage blower used in the rig would drive me nuts even
at half voltage. But running the "Mac" at 400 watts means
everything is cool. |
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Final
and modulator tubes in the BA2.5K. I run the 4X1 modulators in
screen and grid driven zero bias and there is only 50 mils static plate
current on them at 1600 volts. The fil voltage is at 6.9 volts so I
would expect the "tough-to-get" 4X1's should easily outlive me! |
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A
4-400A next to 4X1 for comparison. |
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 Click here for off-the-air audio
of W2ZM describing his Continental 314 while talking on Big Mac.
(Recorded 0730Z, 10-Dec-2005, in Glendale AZ, ~300K)
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