[ARC5] Unstable VFO

[D C *Mac* Macdonald]

Many years ago, one of the ham radio clubs in Oklahoma City
had a guest speaker that I think was employed in ARRL lab.
He presented quite a talk on VFO stability and part of that
talk was the info that POLYSTYRENE capacitors tend to be VERY
unstable beasts and should not be used in frequency determining
circuitry.

Mac, K2GKK/5



----Original Message Follows----
From: David Stinson <arc5 at ix.netcom.com>
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] Unstable VFO
Date: Mon, 02 May 2005 08:34:06 -0500



Ian Wilson wrote:

>Posted a while back about a haunted ARC-5 VFO on 40m. Strange 'warbling'
>instability that I just couldn't defeat despite changing many parts.
>
>Someone - Ken Gordon, I think - suggested a bad joint around the tube
>socket. The answer turned out to be a bad joint somewhere in the grid
>circuit.
>
>The VFO is quite stable now, running from a 182V stabilized (Zeners,
>sorry) supply. The original dogbone ceramic capacitor has been replaced
>with a polystyrene equivalent that appears to be doing a fine job.
>
>This has taken way too much time, need to get the rig back on the air
>now.

Good news.  I think I'll take that suggestion on a BC-459
with a similar problem.

Since we're talking about this, it reminded me of the suggestion
to use ferrite beads to kill VHF parasitics, if that were the problem.
I have a similar situation that is certainly rooted in VHF parasitics.
What is the proper procedure for selecting the "right" ferrite
for a problem?
D.S.
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