[R-390] That's more like it!!!

[Barry Hauser]

I see that Meir answered your first question as he posted his reply to the
list.  I don't see a reply to your second question.  It appears that the
general activity level of the list has diminished.  Part of this may be due
to the practice of replying off-list -- perhaps to conserve bandwidth, keep
a low profile, or, I dunno -- maybe solar flares wiping out the band?
Anyway, there is the tendency to think -- well maybe the guy got his answer,
or I have an idea, but someone else out there is more expert or whatever.
As for the first question -- I, for one, did not know the answer.  As for
the second (about why some guy swapped out the balanced connector for an
SO-239 instead of the balanced one), that sounded like the courtrooms scene
in the movies where one of the sides yells out "Objection!  Calls for a
conclusion!" or conjecture, etc.

Anyway, here goes nothin':

I can't say with any assurance as to why the anonymous modder chose to
replace the balanced connector instead of the unbalanced with an SO-239,
however:  It is/was procedure to ground one side of the balanced connector
when connecting an unbalanced line to the blalanced connector, even when
using a twinax connector on it.  Also, there are adaptors around that
convert from twinax to C-connector (like the unbalanced).  One side of the
twinax is grounded inside the adaptor.  Most (maybe all?) of these adapters
are right angle/elbow shaped.  There may be variants that go to something
other than a C-connector -- perhaps an SO-239 or an N-connector?

So, it may have been a common mod in the functional sense, but doubtful that
many changed out the connector altogether.  If a made-up adapter is
difficult to find, it's an easy matter to make up a twinax to SO-239 cable,
or a longer coax going from a twinax plug (with one side grounded inside) to
a PL-259 plug.

I can offer two theories as to why the Unknown One chose to replace the
balanced connector:  A.  The unbalanced one looked more "normal" and thus
likely to be found one day, and/or B.  Rumor or conventional wisdom had it
that the balanced connection was better.  This may really have depended on
which was used during alignment.  However, any inherent superiority may have
been undone by grounding one side.  Twinax connectors are now commonplace
and cheap as they were used for computer network cabling.  This may not have
been the case or known to the modder at the time.

Of course, this is all conjecture and further persuit may get us into the
areas of Boatanchor Archeology, Boatanchor Anthropology and even, yes ..
Boatanchor Forensics.  These are rather unusual fields of endeavor.
(generally recommended that one keep his or her day job ;-)  On the other
hand, perhaps someone will unearth an article entitled "Replace that Weird
Balanced Connector with a Good Ol' SO-239" among some crumbling scrolls or
musty magazines which would shed further light on the motivations at play at
the time.  In the Day's of Yore it was customary and fashionable to perform
what are now considered abominations upon vintage and historical objects and
there were numerous heretical tracts in circulation.  The pendulum has swung
back in the direction of orthodoxy, such that  authenticity is prized over
practicality,  to the extent that artifacts such as original knobs, tags,
and even dynamotors are much sought after.

If you wish to restore your R-390 (non-A?), you may be able to fit a
standard twinax panel connector, or, if not, get another antenna relay
assembly.  I have a supply of R-390A type available, plus some odd ones that
include a gas discharge tube.  I forget now what the difference is between
the R-390 and R-390A versions.  However, on an electrical/functional basis,
what you have there is a fairly standard setup.

Barry


> ANTENNA INPUT MODIFICATIONS 1/23/2004
>
> On my R-390 someone removed the twinaxial socket on the balanced input and
> replaced it with an SO-239. The center conductor of the new connector
passes
> thru to the high side of the transformer while the other side is now
> grounded. Was this a common mod? why wouldn't you just replace the
connector
> on the unbalanced input with the SO-239?