[Premium-Rx] Watkins Johnson 8940B receivers

[refmon]

Hi to all on both lists.  I'm looking for WJ 8940B drivers out there.  I
have just taken delivery on two pristine units with every obscure piece of
documentation including little notes from the original owner's maintenance
guys.  They even attached mini zip-locks of spares to the associated
diagrams.  Both units work fine.

I do have questions, though.  Aside from a healthy layer of warehouse dust,
these two sets are absolutely clean from a technical perspective.  In
receiving such items, I do a physical cleanup and usually run through power
supplies, non-critical alignments, etc...run them for a while to get the
feel and then go in a bit deeper.  These units are 23 and 25 years old, so
I'm sure a variety of tweaks are in order.

My first lineup of inquiries:  throughout both receivers, I find nominal
master power supplies with regulated outputs called at +10, -10, +20, -20,
28, etc.  These are then regulated down throughout the various chassis as
required.  I find the master supplies consistently high by 2-4 volts and the
local sub-regulated voltages consistently low.  for example, the +20 supply
is set to +23.6 and the alleged sub-regulated +15 is at +14.2.  I've been
brought up to set supplies to nominal within a fairly tight tolerance for 30
years.  Naturally, I am wrought with wonder and conflict.

First, many circuit alignments are directly dependent on supply voltage
absolute value and stability.  So +/- 15VDC supplies should be
+/-15VDC...not +14.8 and -14.2.  Secondly, the nominal raw input voltage to
a sub-regulator should be what it says...too low and it may sag out of
regulation under various loading...too high and the regulator itself may be
stressed in dumping, shunting, or otherwise reducing the raw volts to
regulated volts.

So, in a practical sense, what have users observed in real-world 8940's?  My
initial impression is that this receiver in particular is smart enough to
rework its entire cal tables to compensate for a voltage variation over
time.  What's the practical experience?

Further, one unit is equipped with NBIF (narrow band IF) which goes all the
way to 5Hz operating bandwidth, which works quite impressively, actually.
Along with that goes the low frequency tuner, covering 20Hz - 1KHz....very
interesting indeed.  Then there is the MX unit, a microwave extender for
1GHz through 18GHz.  All things considered, these are extremely impressive
units with the singular exception of packaging, which I guess is pretty much
par for the period.  A two rack width console, 30" deep with one rack set
having a raised, sloped area for the control panel.  Has anyone gone so far
as to repackage these units in vertical racks with, perhaps, a sloped
control area and small table top?  That appears to be about the only way to
fit these guys in a modest shack.

hope to hear from a user or two

best regards

John collins
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