THE 70 CM. 1KW AM SYSTEM
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The 70 CM.(440 Mhz) 1 KW AM transmitter,
is another Air Traffic control transmitter, and it covers the frequencies
from 400 to 450 Mhz after modifications to the line sections. The proper
nomenclature for this transmitter is the T-282,
and a lot of people tried to put them in service as A.T.V. amplifiers.
I didn't need one for that mode (See other descriptions) I wanted to round
out the 1 KW AM equipment to 440 Mhz and I thought this unit would just
fill the bill nicely.
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The transmitter comes with
a built in exciter stage made up of, a 6AH6 osc, 2 multiplier buffer stages
of 5763 tubes,
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and a driver amp which is an 832A. The output is used to drive another
multiplier, which is a single 4CX250B, which
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in turn drives the final amplifier stage consisting of a pair of 4CX250B
in parallel. The unit was originally a screen
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modulated rig with a pair of 6AQ5 tubes modulating the screens of the 4CX250Bs'.
- I modified this unit to allow remote frequency control of the oscillator,
using my "Shop Generator" which provides the 8 Mhz signal for the oscillator
stage. I didn't get the modulator or the power supply decks with this one
either, so they had
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to be designed to handle the various stages requirements. A low voltage
supply provides 400 VDC for the plates of the osc/driver stages. Another
supply provides HV plate at 800 VDC and screen volts at up to 400 VDC and
a 0 to
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100 VDC bias supply for the 4CX250B multiplier stage. The last supply and
the largest is for the final stage
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(2X 4CX250B) and provides 0 to 150 VDC minus for bias, 0 to 450 VDC for
the screens and 0 to 2000 VDC for
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the plates.
- The modulator stage is a class "B" section ending with a pair of 811A modulator
tubes running with 1500 VDC
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on the plates.
- I have pictures of the rack for the 1KW AM 440 Mhz transmitter.