[R-390] Z-503 repair

[bavarianradio at comcast.net]

Hi Paul, I used a variable power supply set to 350 volts DC and a 100 ohm 10 watt resistor. I desoldered one end of both capacitors inside the can and attached the ground lead from the supply to one lead on the coil. I then connected the + lead from the suply to the 100 ohm resister. Then you draw an arc to the other coil lead. I just held it for a few seconds and pulled away, then checked  the DC resistance. I did this a few times until  I got a low ohms reading on the coil.(about 30 ohms) This only worked for a few hours then died again. I did it again  and it seems to be "holding"  I just don't feel comfortable with it. I don't know what solvent will work best. I haven't tried any yet. I do hate MEK , it seems deadly!!! Good Luck!!! 73's Ross W1EKG
----- "Paul Staupe" <pstaupe at qwest.net> wrote:

Ross,
Thanks...In my original question, I refrained from using the "non-A"
designation for my R-390/URR, but to eliminate the confusion, it's a
non-A.
Z503 is also the AGC can in the R-390A model, so using the non-A
description
might have helped clarify my situation.  Looks like Z-503 is a weak link
in
both designs.
A list member is kindly helping me out, but in the interim, I'm thinking
about trying to rewind this one.  Does the varnish respond to acetone or
MEK
or what's the best way of removing it?  Also, what's the procedure to
zap
the coil, presuming that hitting it with HV won't do further damage..
Thanks again to all who've helped out.
Best regards,
Paul W0AD
From: bavarianradio at comcast.net
To: Tisha Hayes <tisha.hayes at gmail.com>
Date: Thu, 10 Mar 2011 15:41:33 +0000 (UTC)
Subject: Re: [R-390] R-390/URR Z-503
Hi Tisha, The problem with Z-503 is that the windings  are encased in a
powdered iron cacoon and then dipped in varnish. I expect that the coil
will
need to be soaked in acetone (or solvent of your choice)  to get it
apart.
 My Z-503 is currently behaving itself but has been intermittent. I
"zapped"
it with a high voltage arc and got it working, but I'm skeptical as to
it's
reliability. My intentions were to find a good replacement and then go
experimenting with rewinding this one. As you suggested, this can't be
brain
surgery.  BTW this coil does not exist in the "A" radios. (I already
looked
at my spare "A" IF deck... rats!) 73's Ross W1EKG