[R-390] Snap Crackle, Pop, and frying eggs

[David Wise]

A while ago I got the snap-crackle-pop symptom - plus loss of gain - and it turned out to be a failing insulating sleeve on a tube socket terminal in the IF deck.  Manufacturing and assembly tolerances had put a bulkhead/shield into pressure contact with the insulated terminal.  After sixty years it finally started to puncture, pulling down the screen grid of one of the IF amplifier tubes.  With sharp eyes and a mechanical probe, you will be able to tell if you are in line for this failure.

The time before that, the culprit was one of the molded mica caps that tune the mechanical filter transducer coils.

Dave Wise

Since my C553 is one of the high-quality hermetically-sealed models, I left it in place and added an LND150 in series to limit the current in the unlikely event of a short.
________________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Tisha Hayes <tisha.hayes at gmail.com>
Sent: Monday, September 18, 2017 8:35 PM
To: R390A
Subject: Re: [R-390] Snap Crackle, Pop, and frying eggs

Another technique you can try when looking for a bad resistor or cap that
is right on the edge of failure. Freeze spray.

First make sure that you are not toasting a filter (the killer cap). If you
use freeze spray and a tiny squirt on a particular resistor or cap you will
quickly find the offender when the snap, crackle, pop radically changes.

*Ms. Tisha Hayes, AA4HA*