----- Original Message -----
From: "Steve Wedge" <[email protected]>
To: "Ron" <[email protected]>
Cc: <[email protected]>
Sent: Tuesday, August 23, 2011 4:43 PM
Subject: Re: [Drakelist] I feel like a buzzard...
completely random. Gets worse if I tap on it, but then
again, I'd expect some reaction when tapping it. Now, I've
got to find some test leads. I'm going to turn my station
supply down to 11V so I can still run the K3 and will power
each PTO off this very stiff supply.
It's now obvious to me that it's either the PTO (yeah, both
of 'em) or the regulated supply has issues.
Steve Wedge, W1ES/4
If the PTO works in one transmitter but not the the
other that pretty much eliminates it. Have you made
comparitive voltage measurements in the two transmitters?
Gary said something about the source voltage for the zener
being marginal. The zener is fed by R-64 which in turn comes
from the regulated 150V buss. The voltage at the other side
of R-64 should measure very close to 10V and be very stable.
Check it using the scope while keying, it should not change.
R-64 is a wire-wound resistor. They are generally quite
reliable and do not change due to age or loading. However,
if one of the terminals gets flaky it can go up in value.
Its worth measuring and should be very close to the marked
value. If it has increased or if the solder terminals
between it and the zener have developed some resistanct the
current drop may be enough so that the zener can not
regulate. Tapping on the PTO may cause some shift in
frequency simply because things inside move a little.
However if tapping produces exactly the same sort of chirp
you get from keying it strongly suggests a bad solder joint
somewhere in the voltage line to the PTO. Trace this out and
poke around at it. But, check the voltage at the zener end
of R-64 to see what is happening there.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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