Bill,
I'm not familiar with the circuit of the FL2100, but your symptom sounds like
there may be an unintended extra shunt that's throwing off your meter readings.
Sometimes that's caused by a protective diode between B- and ground intended to
safeguard against flashovers. In most grounded grid configurations with the
grids tied directly to the chassis ground, the resistor between B- and ground
just monitors grid current. The B- return to the power supply from the tube
cathodes has to be completely isolated from ground, except for the grid current
monitoring resistor. Just a thought.
73,
Jim W8ZR
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Bill & Liz
> Sent: Sunday, April 20, 2014 9:34 AM
> To: amps@contesting.com
> Subject: [Amps] WEIRD ONE!
>
> 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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