[R-390] Update on R390A, open question regarding scope and options fir lubrication

[jkharvie]

 OK,thanks for this good input...!
I do have an option to place a Micamold cap back into the RF circuit

 or I can 
 use a new 1000 volt high Q mica cap that I purchased that will arrive in 2 days.
The new capacitor is a quality RF high Q unit also made by Cornell-Dubilier. 

Also - maybe we need to update the recommended procedures advice page on when to swap out capacitors in the receiver...

thoughts?
  John

    On Friday, June 28, 2024, 11:12:43 AM EDT, Jacques Fortin <jacques.f at videotron.ca> wrote:   

 Hi John,

The mica caps in green plastic shown in your picture were made by Micamold.
I also have few of those in the spare IF modules I have.
But I never found a single one failing up to now.
The mica caps in the C327 position that were reported failing (which seemingly generated the recommendation to change those on sight) were made by Cornell-Dubilier and are older than your "green ones".
IMHO, it is not necessary to replace them all, and maybe the originally used one at the C327 position was perfectly good initially.

Which is very bad in the C327 case is to use a ceramic capacitor which is not a NPO (C0G) one.
And even there, some will not fill the bill, having a ESR value higher than a mica one.
Using a high ESR capacitor in a parallel resonant circuit kills the Q of the circuit and the gain of the related stage.

73, Jacques, VE2JFE in Montreal