[R-390] The adventure begins (and a capacitor question).

[Barry Hauser]

Hi John & gang:


> So my R-390a has arrived.

H'ray!!!

  I know there are things that one should do before
> turning it on.  I checked the fuses and replaced a bad one.

John, I think you skipped a few steps....

  But then I cast
> all caution to the wind and turned it on.

Well, that depends.  If the previous owner said it was running recently
without sparks or smoke (and actually took an oath to that effect) -- then
it might have been safe.  But -- you did mention that a fuse needed
replacing.  Sometimes they just wear out, but other times, a burnt fuse
indicates that something  is wrong.

  I'm not sure if it's completely
> functional.  The line audio stuff doesn't seem to do anything, but it
plays!

Whaddya mean "line audio stuff" -- the meter?/ranges?

> Sounds great through a Klipsch Heresy.

That's a good start -- you're lucky so far.  "Heresy" -- is that the right
model name?  Does it defy accepted acoustical engineering practice?  Or is
the name something like "Heritage"?  BTW, you are using a 600/8 ohm
transformer, right?

  A vintage speaker that's too ugly
> for my living room.

No -- probably more like your living room is not appropriately decorated.
How many 6 foot rack cabinets?  Droplight sconces?  Neon beer signs?

  So the overpriced shipping may have worked out.
>
> It's a little bit moody though.

What do you mean by moody?

  Maybe a lazy capacitor or something like
> that.  So I'm thinking the first thing to do is start replacing
capacitors.

But at least start with the problem ones -- particularly the mechanical
filter killer -- C553 I think.  At least  check it with an ohmmeter, though
that's not much insurance.  I've yet to find one bad, but the consequences
are so steep, I don't take any chances.

> I'm guessing if it's electrolytic, tantalum, or paper, it wants to be
> replaced.

What's it doing, or not doing?

  But my question is, what's the best capacitor to replace the
> paper capacitors with?  Polyester, polypropylene, ceramic or something
else?
> I get the idea that the *orange drop* is popular, but has anybody ever
> thought of using ceramics to replace some of the paper ones?

Orange drops seem to be the cap of choice for most.  Some swear by the
yellow poly's which are true axial and easier to fit in a number of spots.
However, one problem is that they're easily damaged by the soldering iron,
whereas OD's are not.  Also, that heat resistance is somewhat more
comforting during actual use.  Prepare to get some spaghetti tubing or
better yet, teflon tubing for the leads on the point-to-point caps.

  Maybe they are
> even more reliable than the orange drops.  You can get 0.01 uf in a 1000V
> version, and you can even get 0.1uf in a 200V version.

Sounds like you're talking about Radio Shack's.  I think you mean 0.1 at
2kv.  I pick those up from time to time to replace line filter caps.

  So it may be possible to replace all of the papers with ceramics.  But I
don't know if
> it's a good idea.  What do you guys think?

Not recommended.  Later built SP-600's came through with mostly ceramic
disks, but not the cap of choice for R-390A's in most cases.

I'd replace that one cap right away before you burn out the filters.
Unlikely, but you've been too lucky so far.

Some things to check -- try all bands, using the calibrator if necessary or
a siggen.  It's not uncommon to find some are dead -- usually come in 2's
and 3's according to the crystal configuration scheme.  Some of the xtal
decks have rather loose sockets, so get out the DeOxit and do those, tube
sockets and pins, any switches you can reach -- and later on the ones you
can't reach ;-).  Check all the tubes, especially for shorts.  Check the
gear train for grit, gluey grease.  Oh -- with the top off and the "utah"
cover removed, very carefully watch the slug racks as you change bands and
tune through.  Some may be binding on the downstroke.  It's sometimes
difficult to see and you have to press lightly on a rack that's supposed to
be going down to see if it isn't hanging up.  Also make sure the cam
follower rollers are actually rotating otherwise you'll be flat-spotting
them as you tinker around.

Other basic preliminaries -- check the two plugin caps on the audio deck.
Check the mechanical synch using the procedure in the manuals.  Look for any
broken or loose clamps.  Check the range on the KC control end to end.
There are a lot of preliminaries that would logically come before a total
recap job, at least from where I sit.

This is one radio where there's lots to do and look at before listening.
But that's the fun.  Just be careful if someone casually asks "Whatcha doin'
John?" and you answer "Watchin' the radio."  They might take you away.
(There are a number of guys on this list that are unaccounted for. ;-)

Barry