[Amps] WEIRD ONE!

[Bryan Swadener via Amps]

Hi Bill,

The GI-7b has one side of the heater tied to the cathode.
Feeding bias thru the transformer CT results in modulating
the amplified signal with 60 Hz.

A friend did the same thing. Look at http://gi7b.com/
for how to apply bias.

vy 73,
Bryan WA7PRC

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Date: Sun, 20 Apr 2014 11:34:07 -0400
From: "Bill & Liz" <magoo at isp.ca>
To: <amps at 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