[Collins] Deadly caps list for the R388/51J series ??

[Dr. Gerald N. Johnson]

On Fri, 2009-08-21 at 23:54 +0000, John Hensley wrote:
> Has anyone seen a deadly caps list for the R388/51J series ? I am thinking of the list which has been out on the 75A4.  Just wondering if anyone has kept or compiled a list for the general coverage cousin.
> 
> Also, if anyone has an R388 power transformer available please contact me with price & availability.  I now understand why the receiver I bought was such a bargain :-( ...
> TIA, John W5JV
 
All the electrolytics are highly suspect. All the molded oiled paper
capacitors are known leaky. There aren't any mechanical filters to be
destroyed by a deadly leaky capacitor characteristic of the 75A-4. The
mechanical filter adapter does put full DC on the filter input coils
which may not be the best thing for filter longevity, but that's the
circuit design. Plate current for the driving IF stage passes thorough
the filter coil. Postage stamp molded mica capacitors if used (more
likely in earlier 51J) tend to be a little suspect. Worse in 40s vintage
radios, papers were molded to look like postage stamp micas and tend to
be leaky. Bad capacitors, especially electrolytics can be the reason for
the demise of the power transformer. Filter chokes with a short to
ground can be hard on the power transformer too.

There appear to be no molded oiled paper capacitors. All appear in the
parts list to be metal cased, single and multiple units (part number
prefix 961). They have a good record.

The power transformer isn't too exotic except for the case. 115/230 volt
primary (the most exotic winding), 5 volts at 2 amps for the 5V4. 6.3
volts at 5 amps, and 700 volts center tapped at 90 ma for the plate. In
the old days a common radio transformer. These current ratings are from
the schematic, not the parts list. I'm sure Hammond has a stock
transformer for these ratings as did Triad, Stancor, and Thordarson when
the radio was designed.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer