[Collins] R390A-URR

[Dr. Gerald N. Johnson, electrical engineer]

Best I recall (there's much detailed information in the R-390 reflector
archives) if the tag says Collins it was built by Collins. Many R-390A
contracts were supplied by other vendors working from Collins made
drawings. The P in the order number stands for Philadelphia Arsenal
contracting and the 55 I think is the year of the contract. That would
make the chassis construction being about 1956 give or take a year. I
don't think that Collins subcontracted any parts of their contracts,
though they may have supplied parts for later runs with other prime
contractors.

And that all applies to the chassis. The R-390A, being modular, can have
all modules from different vendors and contracts. It was standard
procedure in service depots to disassemble all receivers coming in, then
service the modules on test jigs individually and at the assembly end
assemble receivers from the first modules to reach the end of the line,
totally ignoring manufacturer and serial numbers. So any depot serviced
receiver will have essentially unrelated modules. The design is such
that any random set of modules should work no better and no worse than
any other set. And the design is that serious testing and adjustment of
most of the modules is difficult or impossible without the test jigs.

There are certain mods like replacing the black beauty capacitors that
are practically 100% failed with excess leakage, and to add a low
leakage capacitor in series with the plate connection end of the
mechanical filters. Its important to protect the filters from any chance
of DC current from the plate supply and for overall receiver
performance, especially gain and AGC as well as audio distortion to
replace all the molded oiled paper capacitors in black plastic
cylindrical cases. The oiled kraft paper was not very good and turned
leaky 20 years ago, and won't improve with time. I prefer Sprague Orange
Drop mylar insulation capacitors, their orange dip having proven to have
a very good survival in adverse conditions, though the leads leaving the
corners of the package instead of the middles of the ends makes fitting
sometimes a bit of a bother. Other capacitor makers have made similar
capacitors, but I've not tested those others as stringently.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.