[R-390] Capacitor Replacements Vitamin Q

[Cecil Acuff]

My opinion....

The R-390/URR was what we know as "Military Grade".

The R-390A is more closely "Consumer grade" as far as their capacitor 
choices were concerned.  I have seen as many problems with the Brown 
Tubulars as the Black ones.  I have several cracked in a radio I'm working 
on right now.  It's not an SJC survivor either..before someone throws that 
flag...

Approach the suspect accordingly...

My usual approach is to do a sample test of caps in places that are not 
critical.  If a high percentage come back leaky at rated voltage then a 
wholesale replacement of "Paper" caps is in order.  I'm only speaking of 
paper caps not micas or others that are known to be fairly reliable.

Cecil
K5DL
----- Original Message ----- 
From: <bavarianradio at comcast.net>
To: "Tisha Hayes" <tisha.hayes at gmail.com>
Cc: <r-390 at mailman.qth.net>
Sent: Monday, January 24, 2011 11:50 AM
Subject: Re: [R-390] Capacitor Replacements Vitamin Q


>I agree on this type of equipment where the Mil spec aspect of components 
>kicks in. Consumer grade radios are another can of worms. I'm planning on 
>checking all of the resistors for out of tolerance ones and replacing where 
>necessary. Thanks!!! Ross W1EKG
> ----- "Tisha Hayes" <tisha.hayes at gmail.com> wrote:
>
> A good rule to follow is to replace what is proven bad and leave the
> rest
> alone, unless you have good reason.
> Good reasons to replace capacitors;
> 1) They are paper
> 2) They are BBOD's
> 3) They are way out of spec
> 4) It is the "killer cap" on the mechanical filters
> Wholesale replacement may sound like a nifty idea but you can end up
> with a
> radio that is seriously out of alignment if those caps are in the RF/IF
> deck.
> I have tweaked with capacitor values in the audio section to improve
> frequency response and done a few AGC mods to eliminate the "moment of
> silence". Sometimes I change cap values in the B+ supply to reduce
> ripple
> (Chuck Ripple <g>, <j/k>).
> To a large extent, there is a similar set of rules for the wholesale
> replacement of resistors.
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