[Johnson] Ranger 1 Question/Problem

[Jerry K]

Makes sense to me, Glen. I don't relocate them anyway, I just change out the
original carbon unit with a 7.5 watt 18K Dale wirewound, and that seems to
work just fine. Doesn't change the wattage inside the VFO cage, just spreads
it out a little. Ha. Hope folks don't get the idea they don't have to do
anything about R3, though. It will fail for certain someday, and it's
failure mode will invariably be decreasing R, with a resultant increase in
load on VR tube, and concurrent increase in I as the poor overworked VR tube
works it's little guts out trying to keep up, which of course increases the
current through R3 again, which increases the heat, which increases rate of
R decrease, ad infinitum. A classic vicious circle, and the eventual result
is not pretty, as documented by some photos floating around the web.

I've never taken out an original R3 that was anywhere close to 18K. I've
only restored 5 or 6, but they were all 6K-10K or so in those. I've been
lucky, though, none of the boards were fried (yet) although a couple had
some dark color in a circle around the tube. Of course, when this thread
comes up, somebody always pipes up that he's never had to remove the cover
on his VFO and it still works fine, so no need to worry.   Ok... :-)

Jerry W5KP


-----Original Message-----
From: johnson-bounces at mailman.qth.net
[mailto:johnson-bounces at mailman.qth.net]On Behalf Of Glen Zook
Sent: Friday, April 01, 2005 10:38 AM
To: Jerry K; Bruce J. Howes; johnson at mailman.qth.net
Subject: RE: [Johnson] Ranger 1 Question/Problem


If that is the power resistor in the VFO compartment
there was a discussion on a couple of reflectors about
this.  It seems that removing it from the VFO
compartment actually causes more drift when outside of
the compartment than within the compartment.

The temperature compensation for the Johnson VFOs was
done with this resistor inside the VFO compartment and
removing it actually upsets the compensation resulting
in more drift.

Several amateurs did frequency stability tests with
the resistor both inside and outside of the
compartment.  Every one of the results were the same:
Considerably more drift when on the outside.  The
comparisons were made from a cold start through
several hours of operation.  It was surmised that
Johnson put the resistor inside the compartment to
temperature stabilize the VFO sooner and for long-term
stability.

Glen, K9STH


--- Jerry K <w5kp at direcway.com> wrote:

First question everybody will ask: Has the
anti-Chernobyl mod (18K R3 relocation/replacement)
been done?
> If not, this is not good.

Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco



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