[R-390] ReCapping R-390A

[Dan Merz]

George,  when I got my 390a I sort of did what you did.  I took a look inside
and assessed what looked bad.  My basic approach is "if it ain't broke,  don't
fix it."  But I gave in to the idea of replacing the critical cap in front of
the mech. filters just because that didn't really take much work and there's
nobody that says it's not going to fail eventually with serious consequences.
I replaced a few others but more or less when I could tell there was a
malfunction.  There is one physically small,   cathode bypass cap,  in the audio
section as I recall,  that invariably seems to be bad and it's condition can be
spotted and I replaced that.  And I replaced the plug-in power supply caps. So
far the receiver has operated pretty well.   I would say completely recapping
the whole receiver is a bigggg  job.   My 390a is one of the later EAC types so
I expect it might have more life in the original parts than some of the earlier
versions.  I have no  experience with earlier versions so that statement is
based on intuition and occasional statements from others to that effect.  The
general consensus seems to be that the black IERC actually cool the tubes,
whereas the others are more or less ineffective,  if not worse than no shield as
far as cooling goes.   Dan

"Kavanagh, George" wrote:

> All:
> Well there _are_ a few newbees out here (me for one), and I'm _very_
> grateful to those list members who have gone before and for their
> willingness to document and share their vast amount of R-390A knowledge and
> lore.
>
> I obtained a Collins R-390A last month (Serial#3319 of Order#8719-P-55).  It
> was "known good" by its previous owner, so I fired it up and delighted in
> its features and operation for several weeks).  I've obtained the
> documentation (Y2K, Rev2, etc.) to which list members directed me, and have
> begun to digest it.  Having discovered the potential of a lurking timebomb
> in C-553, I resolved to open up the box & see if it had ever been recapped.
> After purchasing a set of Bristol Spline L-wrenches (from McMaster-Carr) I
> removed the IF subchassis and discovered that no recapping had been done.  I
> think.  There are several "VitaminQ" caps in the IF  ( C531, 533, 536, 547,
> 548, 549) but C-553 is _not_ a "VitaminQ", it is marked "ASTRON" "TQFP 4982"
> ".01 mF 300 WVDC".
>
> ** I'm sure that this C-553 should be replaced by an OD, as recommended, but
> am curious: was this ASTRON cap factory installed?
>
> Also, the shaft coupler on the Bandwidth shaft was a real bear to loosen; I
> was afraid I would strip out my nice new spline wrench!  In the end, a drop
> of LiquidWrench on the coupler's nut, and a touch of heat from a soldering
> iron on the nut did the trick.  I don't think this thing has been opened up
> in 50 years!
>
> ** All the tube shields are silver colored.  I have read that Collins
> started using black IERC shields at some point in production - when was
> that?
>
> Recent posts to the list suggest replacing all brown color-banded caps - the
> IF has 11 of these, several in quite inconvenient locations that would
> require significant disassembly to do properly.
>
> ** Just how big a project _is_ completely recapping an R-390A?
>
> Thanks for any & all comments and suggestions
>
> George Kavanagh; KB1HFT
>
>
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