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Author Topic: Heathkit Comanche Transmitter Mods  (Read 1362 times)
JAMES_BENEDICT_EX_N8FVJ
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Posts: 692




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« on: February 24, 2003, 09:20:24 AM »

The plate blocking & shunt capacitor at the B+ side of the RF choke are not of a heavy duty design. After the years of use, they need replacing. After new 2.5KV parts were installed, the transmitter tunes better & produced 5 watts more carrier output. I simply drop the carrier back to about 12 watts & have modulation to about 70 watts output. This is using 630 to 650 volts DC input. Do not apply over this voltage or arcing will occur on the plate air variable capacitor. The Heathkit HP20 Utility power supply has two 100 ohm @ 10 watt resistors placed in series with two capacitor banks. The 10 watt rating is a little too low & the power supply outputs about 700 VDC under average load with these resistors. I replaced the resistors with 120 ohm @ 20 watt resistors & installed a 20 ohm @ 10 watt resistor in the high voltage output. This reduced the voltage to about 650 vdc & under modulation maintains 630 vdc. The transmitter is rated 600 vdc input.
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