[Johnson] Invader VFO Modification

[james.liles at comcast.net]

Good morning David:

If drift is a problem, the Invader VFO has a unique drift adjustment.  I don’t 
believe it is addressed in the alignment procedure.  The only other VFO that 
I have seen the same implementation is the Hallicrafters SX-115.  The Hal 
designers do not want you to touch them.  It is actually an easy but time 
consuming adjustment.

C55 is a differential cap that uses C53, a 22pf NPO and C54 a 22pf N750 cap 
to align the minimum drift to band center.  The drift will increase toward 
the band edges because of the positive drift attribute of the tuning cap.

Measure the drift at 2, 15, and 75 minutes at the low, middle and high 
frequency settings --- would be interesting to hear what they are.

Kindest regards Jim K9AXN

------------------------------------- ORIGINAL 
MESSAGE --------------------------------------------------

Date: Sun, 04 Aug 2013 13:45:51 -0400
From: "David C. Hallam" <dhallam at knology.net>
To: Johnson List <johnson at mailman.qth.net>
Subject: [Johnson] Invader VFO Modification
Message-ID: <51FE934F.8070004 at knology.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Has anyone had any experience with the X-Lock 3 VFO Stabilizer?

http://www.cumbriadesigns.co.uk/x-lock.htm

I am considering carrying out the Johnson recommended modification to
the Invader VFO, but it is a PITA job to do.  The X-Lock stabilizer
appears to be an easier modification to implement and probably more
satisfactory than moving existing components around as Johnson outlines
in their procedure.  I am guess that it would allow the elimination of
the always-on VFO heater too.

David
KW4DH