[R-390] Is anyone selling R-390A Cap kits?

[Cecil Acuff]

Well now you gone and done it...

I agree with your statement about mil qualified paper caps if you are 
talking about the R-390/URR.  Not so with the cost reduced R-390A.  The caps 
obviously were approved by the military for use in the R-390A as offered in 
the cost reduced receiver.  The caps are not any better than those offered 
in the SP-600 or any of my Hallicrafters receivers with the Red Chiefs. 
Failure rates are pretty much the same...

I'll be happy to ship you a box of them if you like...all fail the leakage 
testing on the Sencore cap analyzer which means they have developed a 
resistive component.  One that can be present at any voltage that cap may be 
subjected to in it's normal use.  Once that process starts within the cap it 
only progresses.

It doesn't matter if the receiver was in a rack for it's life or sat in the 
pile at St. Julians creek.  The outdoor exposure may have tended to 
accelerate the process but a process it is.

My suggestion is to lift one end of a sampling of the caps and test them 
with an appropriate tester and replace those that fail.  Replace the cap 
that protects the mechanical filters regardless and use a higher voltage 
rating on that on for added insurance.

In the event that you don't have an appropriate cap tester and don't plan to 
do several other receivers as part of your hobby endevours, then replace all 
the caps and be done with it.  Do the work slowly...replace a few and test 
the receiver...do a few more and test the receiver.  This process will help 
you identify a problem you may introduce in the process of changing the 
caps.  If you are an experienced tech you may be able to just do them all in 
one fell swoop.

Either way you will have bonded with your new receiver for a life time of 
enjoyment!

Also to answer your original question...Walter Wilson who is a member of 
this list may still have the cap kits and also the nice stainless hardware 
kits to replace all the screws in the front panel if you are refinishing it.

Good luck Bob!

Cecil
K5DL

----- Original Message ----- 
From: "2002tii" <bmw2002tii at nerdshack.com>
To: <R-390 at mailman.qth.net>
Sent: Saturday, September 03, 2011 3:09 AM
Subject: Re: [R-390] Is anyone selling R-390A Cap kits?


> Bob wrote:
>
>>I have an R-390A that is in desperate need of a cap overhaul.
>>      *     *     *
>>I trust Orange drops are OK or should I use something else?
>
> 1).  Unlike many other boatanchors, 390As were built with
> mil-qualified caps.  The mil-qualified paper caps have exhibited much
> lower failure rates over time than the commercial paper caps used in
> other radios (e.g., SP-600).  Consequently, except for the few "high
> risk" caps, I very much doubt that your 390A needs wholesale cap
> replacement unless it has been subjected to extremely unusual
> conditions (in which case, the caps would probably be the least of
> your worries) or was manufactured using commercial caps (there may
> have been production runs with commercial caps, but I don't know of
> any off the top of my head).
>
> 2).  If you insist on shotgunning the caps anyway, Series P225 Orange
> Drops are better than the original paper capacitors.  However, if you
> are going to the trouble to replace them, you can improve the
> bypassing if you replace the paper bypass capacitors with 1 kV disk
> ceramics instead of ODs.  Most of the caps in the radio are bypass
> caps.  However -- NOTE: do NOT replace AGC time constant caps or IF
> or AF coupling caps with ceramics.
>
>
> Best regards,
>
> Don
>
>
> Copyright (c) 2011.  Not for redistribution
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