[R-390] Mica caps and problems

[Perry Sandeen]

Yo Dudes!
1. There are free on line calculators that will do both series and parallel LC circuit calculations. 

2. Considering the age of our receivers one can expect that some micas may be failing or are gradually changing values.
3.  One should consider the prospect that a wholesale replacement may be prudent or becoming necessary in the coming years.  Yes, a wholesale cap change is a PITA but is far less than having to find and change defective caps on a regular irregular basis.
4.  I purchased quite a few micas from Dan's small parts.  He had several package deals that made them quite affordable.  Either with Dan's or just radios there's a minimum plus shipping.  It's just the cost of doing business.
Many subtle and maddeningly difficult problems to solve have been found to leaking bypass caps.  Buying a complete set for the *A* from just radios could turn out to be a prudent move.
Many people on this list see to believe that the small caps and resistors in our B/A's are going to last forever.  It wasn't so when they were made and it will never be so.  

One item that was never in the original specs was an extended lifetime performance specification.  This is because all involved realized that technology would progress and at some future point thy would be replaced.

Now as they get older, just like us geezers, they are going to require more maintenance.
Just because your receiver is *working* doesn't mean its working well or to the optimal OEM specs.  With many good documented mods it can become so much better.  The late Chuck Felton made a living proving this.
Also some sensitivity measurements made with the venerable HP 606 arn't valid as it leaks.  Now sensitivity isn't the only important receiver parameter but it happens to be the easiest to do.  If one wants real and repeatable information one needs one of the better HP or Tek signal generators from ebay.  They cost from $400 on up. (And yes I have two so I can verify their output values are accurate.)
Regards,
Perrier