[R-390] paper capacitors

[Roger Ruszkowski]

Cecil,
 
You are so right.
We tell every new person that comes along to the reflector here to open up 
the IF deck and check C553, the B+ blocking cap on V501 the first IF tube, to see that it has been changed out
before the original shorts out and
takes out the mechanical filters.
 
We know from experience (been there done that) that that specific cap type
being 50 plus years old is failing big time and often enough to be a legend in its own time.

Then we turn and say hay but leave the other 20 of them right where they are and wait for them
to fail for you one at a time. Long before one goes full short or open on you they will start leaking
and you loose filtering and signal strength and start sucking B+ that upsets stage gain performance 
and stresses other parts.

Its not like its a bunch of us R390 fanatic's hung on a vendetta against the sacred black beauties. The  Hammarlund, 
Hallicrafters, National and Racal  fanatic's  are also in the know on this subject.

We have a lot of folks that run their toys from minimum repair to the next failure.
The idea that twice each year you should give each of your toys at least four hours of loving touch is
is not a well supported philosophy or actual behavior. If you do nothing more than blow out some dust and
wash the face plate, give your toys some preventive maintenance at least twice each year.
That's calendar days not operating time.

Once you reach the point where you are forced to pull a subassembly, then give it the full
Monty while you are at it. Do the repair as needed. Deoxit the tube sockets and other connector pins and switch contacts.
You may even give the whole  subassembly / module a dry bath.
 
And if it still has those known suspect parts, warm up the solder iron and change them out.

One of the other Fellows wrote that most of these receivers are not museum pieces and we
are lucky to still have them working as well as they do.

I agree with all of that.
So lets get on with preventive maintenance as opposed to remedial maintenance.

Roger Ruszkowski AI4NI

 
-----Original Message-----
From: Cecil <chacuff at cableone.net>
To: Bob Camp <kb8tq at n1k.org>
Cc: R-390 HF Receiver List <r-390 at mailman.qth.net>
Sent: Sun, Nov 30, 2014 11:48 am
Subject: Re: [R-390] paper capacitors


What's strange to me is that if we were having this discussion on a Hammarlund, 
Hallicrafters or National list it's pretty much an accepted fact that one of the 
first things one would do in a restoration would be to replace the paper 
coupling/bypass caps...black beauties, brown beauties, tiny chiefs you name it.  
But we continue to debate the issue as it relates to the "A" series of the R-390 
receiver when in truth the paper caps used in its build are of only marginal if 
any improvement over those used in consumer grade communications receivers of 
the same period.

It's even accepted that all the Hunts brand coupling/bypass caps in the military 
Racal RA-17 series have to go due to electrical leakage issues....(ask me how I 
know)

What makes the R-390A special (read exempt)?

Cecil

Sent from my iPad

> On Nov 30, 2014, at 9:41 AM, Bob Camp <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> This is why I cringe a bit when people decide to wholesale re-cap some of 
these radios. The parts in there have made it past infant mortality and various 
instal / damage issues. You are trading one set of things for another. 
> 
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