From: Ron Wagner 
Subject: Re: [Drakelist] a dumb question (or 2)


Ken,
The practice of backing off the bias is okay, but runs the finals closer
to class c (as I understand).  Therefore your note will actually have the
potential of being "sharper" on the edges.  In reality the finals are a
miniature grid fed linear amp.  The 12BY7 is the "tranmitter" driving your
linear finals.  You can actually take TX from the 12BY7 if you like QRP.  
Looking into the 2 and 6 Meter tranverter documents that Drake sold 
will show you how to do that.  You will need a matchbox with output 
monitor to take the ~50 ohm output of the 12BY7 into an antenna.

My guess, and it is just that, is that the voltages in your power supply
are moving (the low voltages, +250 and bias).  I would also suggest that 
you check your resistors R30,31.  They are like 68 ohm and I seem to remember 
that they move with age.  I would also look at the 12BY7 driver.

Just a thought.  Have you tried to tune up, and then let the TX set for 
say the day and check again?  That would let you know if it is something 
getting warm from the heating components, or if it related to actual TX 
usage.  Would at least give you something to start with.

Regards, 
Ron  WD8SBB
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Amateur Radio Station: WD8SBB - Ron  and  KB8NRP - Joann
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