[R-390] RF Deck B+ short (390A)

[Charles Steinmetz]

Drew wrote:

>The "filter killer" cap (C-553) in the R-390A is of the same type as 
>the metal cased glass sealed caps of the R-390/URR (aka "Vitamin 
>Q"). Is there something special about the R-390/URR which precludes 
>the possibility of these caps failing?  Is there something special 
>about the R-390A which causes rampant failures of these 
>caps?  Perhaps it is Murphy's Law, given the value and unobtanium 
>status of the R-390A's mechanical filters.

The reason for replacing C-553 is not that they are especially 
failure-prone (at least not in my experience, which extends to a 
couple hundred 390As).  It is that they have been known to fail 
(though very rarely), and a failure is very costly -- normally at 
least one mechanical filter (and often all of them, as the owner 
systematically tries each one while trying to diagnose the deaf 
radio).  Replacing it with a nice, fresh, 600v film-and-foil is just 
good insurance.

Best regards,

Charles