[R-390] capacitors and suppliers

[Dave and Sharon Maples]

All: The  note from Charles seems sound to me.  On the R-390A I did, I went
the all-OD route and regretted it almost instantly.  I had the experiences
that he cited.  Never had the courage to go into the RF deck, so mine is
still "incomplete" I guess.

The only places that seem to sell real film-and-foil caps, though, are some
rather esoteric hi-fi  places.  If there are better sources, I'm all eyes.
When I check manufacturer's websites (e.g. Vishay) I don't seem to find the
real film-and-foil caps still being manufactured as a product line.  I will
freely admit that my search has not been exhaustive.

Thanks,
Dave, WB4FURb

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of rbethman
Sent: Thursday, May 29, 2014 3:27 PM
To: 390 list
Subject: Re: [R-390] capacitors and suppliers

Consider the issues that we went through.

Bob - N0DGN


Charles wrote: (3/2/2014)

If someone is going to the trouble to put together a re-cap kit, PLEASE get
1kV ceramics (X7R or X7U) for all bypass capacitors, and 600v film-and-foil
(NOT metallized film) caps for the few coupling caps (for example, genuine
SBE/Vishay/Sprague Orange Drop P225 Series -- but watch out for metallized
film "orange dip" imposters sold by some vendors). 
Also use film-and-foil caps for the AGC capacitors, but you don't need 600v
parts there -- 100v is fine.

The ceramics do the job much better than any plastic cap in bypass
applications, they are much easier to squeeze into the tight spaces in a
390A, and they are much less expensive as well.  Some of the money saved can
then be invested in getting high-quality film-and-foil caps for the
non-bypass applications without the total cost getting out of hand.  And the
radios so equipped will have the best parts available for each spot.

A kit should also come with 10 feet of teflon (and only teflon) spaghetti
tubing to fit the capacitor leads.

All that said, I am generally NOT a fan of replacing capacitors
shotgun-style in a 390A.  I have looked after several hundred of them in my
day, and am still in touch with the owners of many of them.  With a few rare
exceptions (notably, radios that had been underwater for a time or were
otherwise badly abused, and a very few that seem to have been built with a
bad batch of caps), the 390A does not seem to suffer from serial capacitor
failure.  So, I believe the best approach is to replace the few known
troublesome caps and then just run the radio.  If you have two or three cap
failures within a few years, then you might conclude that you have one of
the rare, failure-prone exceptions and consider wholesale replacement.

The above does not apply to the electrolytic filter caps, IMO -- at the
first sign of trouble, I'd replace all of them with brand new,
high-reliability, high-temperature aluminum electrolytics.  At this point
(2014), the best commonly available (in the US) high-voltage aluminum
electrolytic caps seem to be the United Chemi-Con "KJX" series. 
  For low-voltage applications (<= 50v), the United Chemi-Con "EKZM" 
series seem to be the best.  Mouser has both, as most of the major parts
distributors probably also do.

In brief response to those who may ask, "Why not shotgun the caps -- there's
nothing wrong with improving the radio, is there?":  To change the caps in a
390A, you are working in very tight quarters, and some of the caps are
attached to standoff terminals that are quite fragile and hard to obtain
these days.  It is almost certain that a person with average electronic
construction/repair skills will burn a bunch of wires with the soldering
iron and break a few standoffs in the process of replacing all of the caps
in a 390A, as well as knacker a few other things along the way.  "If it
ain't broke, don't fix it" is a valuable piece of advice taught by those
with lots of experience.

Best regards,

Charles
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