[R-390] starting R-390 restoration

[k2cby]

I am sure most of you will regard this is heresy, but here’s my two cents
worth.

First of all, by all means DO REPLACE the “killer capacitor” C-553 .01 µF
300 dcwv in the IF deck immediately preceding the mechanical filters. That
should be first on your list. On the other hand, don’t go “hog wild” about
the voltage rating. Collins spec’d 300 wvdc, and I don’t see much point in
going over 400 wv. This goes for the rest of the capacitors in the set. The
Collins engineers designed a receiver that would give reliable performance
from the Arctic to the Sahara regardless of wither it was connected to mains
power or a flaky generator delivering anywhere between 90 and 150 volts. 

I have, however, added inrush current protection in the form of a CL-80
varistor, and the receiver is plugged into a surge-protected outlet.

Second, there’s nothing whatever wrong with “Orange Drops.” They are fine,
high-quality capacitors, and I used them when I recapped my own R-390A.
Let’s face it, however, Orange Drops were not designed for RF service (nor,
for that matter, were the “Brown Beauties.”). For my money, it makes a lot
more sense to replace the “Brown Beauties” with ceramic capacitors in all of
the RF applications. The “Brown Beauties” were axial and tubular. Orange
Drops are radial and stand out like sore thumbs, so matching the original
appearance isn’t an issue. Ceramics take up a heck of a lot less space, have
far better performance characteristics at RF, and are outstandingly
reliable. They were my first choice which I re-capped my SP-600.

That said, I would still use Orange Drops in the audio stages, mainly
because they are more economical than anything else in the higher values.
One vital point:  C609        ELECTROLYTIC: 8 µF, 30 dcwv. wet tantalum
capacitor is as bad for the Audio subchassis (it leaks corrosive gunk) as
C-553 is for the IF subchassis. Replace it with a 10 µF, 35 dcwv
electrolytic or a tantalum (if you want to travel in style).

STAY AWAY from the corrector stack on the PTO unless you are prepared to
make a career out of adjusting it. Been there. Done that. Gave up. Parted
out the PTO.

I have rebuilt the R-390A gear train. Given a good manual like the “Y2K” is
it not a forbidding experience if you take your time. On the other hand, I
wouldn’t do it unless there is a good reason to.

Other than re-capping, take time to be sure that the switches – especially
the bandswitch – are clean and sparingly lubed.

My last piece of advice is that the R-390A is a modular radio. Don’t try to
do everything at once. Work on it one module at a time. Start with the power
supply if you are going to replace the 35W4s with solid state rectifiers.
Then go on to the audio deck. Then the IF deck, which will take up the bulk
of your time. The crystal oscillator comes next. Finally, the RF deck. After
each stage is completed, plug the module back into the main chassis and make
sure the radio still works! 

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400

Fax.: (631) 725-2223
e-mail: k2cby at optonline.net