[Amps] WEIRD ONE!
Bill & Liz
magoo at isp.ca
Sun Apr 20 11:34:07 EDT 2014
I just finished a GI7-B conversion of an FL2100 to 6M. Everything works fine with good output and no anti-social habits to this point. BUT there are two issues the solutions to which have eluded me so far:
1-Upon key-up and with no drive applied, I have almost no idling current on the meter (between B- and ground across a shunt). The tube is cut off in RX and in TX a variable bias is applied via a bias board to the CT of the filament transformer. The resistor shorting relay works and the bias changes from about –22V to around –6V (it is variable). I should see about 40 ma of idle current, not the width of the meter needle.
2-With about 250W output measured on a Bird with 500W slug 25-60 mhz, I see only about 100 ma on the meter when, for that output, I should be seeing perhaps 250-300 ma. The meter shunt is good and the meter/shunt combination has been tested in my meter test jig. A 0-300 ma meter was substituted (with no shunt) with the same result.
Now, one clue may be that the fan slows down as I tune the amp, suggesting that RF is getting into either the fan or its 12V power supply (possibly the meter circuit too???). I am working on that with more by-passing and shielding. But what could account for the almost nonexistent reading of idle current in a no-drive condition?
Any ideas here? What have I missed?
Bill VE3CSK
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