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Gates FM-1B Transmitter

R

RFJUNKIE

Does anyone have experience with a Gates FM-1B transmitter? I have an issue with ours. I am unable to maintain a decent screen current, on one tube, when the tx is operated at less than a killowatt. Any help is appreciated.<P ID="edit"><FONT class="small">Edited by RFJUNKIE on 11/27/05 10:30 PM.</FONT></P>
 
I worked on a 1C, which I had a difficult time getting a kilowatt out of.

I presently have a 2.5H on one station, which we originally operated well below the rated 2500 watts because of a high antenna & some short spacing. To get the transmitter to be stable at thelicensed tpo of 1200 watts required changing a tap on the plate transformer to lower the plate voltage, as well as adjusting the bias.

The manual probably has information on doing this, but that manual probably has long vanished. Right? However, you may be able to find information on the tube's operating characteristics on the net which may prove helpful. I recall the 1C used something like a 4-400 (?) It was a ceramic tube (long time ago).

By the way. On both the 1C and the 2.5H have had problems keeping the IPA happy. One day the IPA in the 2.5H shorted the 700 volt supply which also supplied screen voltage to the final. In an emergency, I connected our MX-15 directly into the final and discovered that the IPA (at 1200 watts out) was putting out less power than was going in from the exciter. We now use a Continental 802A to drive the final directly to get new licensed tpo 0f 2400 watts. Requires about 20 watts drive into the 5Cx1500B.

Your final is different of course, and if you try this trick with the 1B be sure and "T" a shorted quarter-wave stub into the feed from your exciter to the final. Best done with a modern solid state final with some tolerance for fluctuating load, as there will be high vswr when the final is not working.
 
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