[R-390] AGC voltage issue

[David Wise]

Ryan wrote:

>>So this C551 on my good EAC IF Deck:  When I removed it from the circuit it
>>has 0.6V across it.  When you short it, the voltage goes away.  When you
>>remove the short, the voltage is back.

Charles replied in part:

>As ever, I caution against using a
>metallized film capacitor -- use only a film-and-foil cap like a
>Series 225P Orange Drop or equivalent (for much more on this, search
>the archives for "film-and-foil" and "self-healing").

Self-heal events (characteristic of metallized film) are harmless in C551, the AGC Time Constant cap.  It's C553 (mechanical filter coupling) that needs to avoid them.

By the way, if you're replacing C551, look up my mod that removes the "Moment of Silence" behavior.  It's in the Y2KR3 Manual, chapter 11.  It abandons the original cap, which saves you the aggravation of restuffing it.

Dave Wise

I too have seen caps playing "battery".  In my case it was an electrolytic.  I guess that impurities attacked the electrodes.  I would never have noticed except it was upsetting a low-level DC circuit.  (Galvanometer section of a Fluke 540B AC Transfer Standard.)  In your case, it's innocuous, but the leakage that is certainly also present is a deal breaker.  Terminate with prejudice.