[R-390] Caps

[rbethman]

On 4/25/2013 4:11 PM, Charles P. Steinmetz wrote:
>
> Yes.  I've tested several types of Panasonic PP caps and found 
> unacceptable self-healing events.  If you insist on using metallized 
> film caps, the Panasonic ECWH(A) series of 800 volt parts is about as 
> good as you can do.  But why, when it is just as easy and only a 
> little more expensive to use film-and-foils?
>
> And again, for the vast majority of caps in any boatanchor -- power 
> supply bypass capacitors -- why would one use film caps at all?  1 kV 
> disk ceramic caps perform better in this application and are extremely 
> reliable, besides being small and therefore easy to install.
>
> If one is going to invest all the time and effort to replace lots of 
> caps, it seems only sensible to use the best parts for the job unless 
> they are prohibitively expensive.  And neither film-and-foils nor disk 
> ceramics are.
>
> Finally, why shotgun the caps in a 390A in the first place?

Have you looked at a '51 contract Collins? (They came out in '54.)

They are full of Black Beauties!  I believe that they are an automatic 
replace item!  It has been beat to death and shown that BBOD is indeed 
the appropriate name!

Sprague Vitamin Qs are fine if they don't test bad, and I haven't found 
a bad one yet.

Later contracts such as EACs had good caps put in them to begin with.

> There is no pattern of general failures in 390As (unlike Hammarlund 
> SP-600s and other BAs that are notorious for cap failures).  Remember, 
> by far the greatest number of lifetime failures of capacitors (as well 
> as most other electronic components) happen in the first few hundred 
> hours of operation. You are at least as likely to install a cap that 
> fails sooner than the one you removed as you are to extend the time to 
> failure.  Of course, if the particular radio has a history of cap 
> failures, it could indicate that the manufacturer was using a bad 
> batch of caps when the radio was built, or that the radio has 
> experienced environmental stress in its lifetime, in which case 
> wholesale capacitor replacement may be indicated.
>
> Best regards,
>
> Charles

Bob - N0DGN