If you are not turning the dial and it jumps then it is not likely a
mechanical issue. As stated before the vfo oscillator is quite
voltage sensitive. My bet is the Zener as I have written earlier.
Solid state devices were not consistently uniform as they are now and
with use can get into an unstable part of the curve and exhibit an
inconsistent impeadence and hen e the jump.
Suggest you change the Zener
Sent from my iPhone
David Assaf, III
On Aug 24, 2010, at 10:22 AM, "steve white" <sswh...@mchsi.com> wrote:
Dennis
I had this problem once in a old HQ170 and it turned out to be the C
in the vfo LC circuit. It was a nice looking mica capacitor and I
didn’t think at first that it could be the problem but after all the
other things I changed once I replaced it all was right with the wo
rld again.
Steve NU0P
From: drakelist-boun...@zerobeat.net [mailto:drakelist-
boun...@zerobeat.net] On Behalf Of Dennis Monticelli
Sent: Monday, August 23, 2010 23:59
To: pony...@aol.com
Cc: drakelist@zerobeat.net
Subject: Re: [Drakelist] unstable R4C PTO
Zener diodes can develop an instability in their voltage "knee"
value due to migration of mobile charge at the surface of the
semiconductor. A random walk of a few tens or hundreds of mV could
produce your frequency problem. Put a scope probe on the zener and
set your scrope for high sensitivity. See if you observe a "jumpy"
voltage.
Dennis AE6C
On Mon, Aug 23, 2010 at 6:37 PM, <pony...@aol.com> wrote:
Hi Gang,
Thanks for all the replies to my past message, but at this point
in time, I'm even more dumbfounded than ever. So far I have cleaned,
and oiled the mechanical parts, installed a ground strap on the PTO,
resoldered all the ground wires inside. everything is free, and
working as it should. Also, I drilled another hole in the cover to
stretch that angled spring giving more tension.
No avail, now I think it must be an electronic problem, as
sometimes, when I try to tune a station, it warbles, sometimes while
I am just listening hands off. vibration doesn't seem to change
anything.
Someone emailed me suggesting the zenner diode could be the
culprit. I always thought most solid state devices either work, or
don't work. Is it possible that's the problem, or could it be
somewhere else outside the PTO?
Thanks for reading this....................Tom, WD8JPP
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