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Re: [Amps] WEIRD ONE!

To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] WEIRD ONE!
From: Bryan Swadener via Amps <amps@contesting.com>
Reply-to: Bryan Swadener <bswadener@yahoo.com>
Date: Sun, 20 Apr 2014 11:54:17 -0700 (PDT)
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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

----------------------------------------------------------------------

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