[Milsurplus] [Boatanchors] URM25

[Paul Kraemer]

Robert
Both carry the nomenclature AN/URM-25J on the case and SG-85C/URM-25D on the 
instrument
They both have the power supply PP6106/URM-25J
Two different manufaturers
I don't see any 12vac in the supply, just 6.3v
Paul K0UYA


-----Original Message----- 
From: WA5CAB--- via Boatanchors
Sent: Sunday, October 12, 2014 2:10 PM
To: boatanchors at mailman.qth.net ; milsurplus at qth.net
Subject: Re: [Boatanchors] [Milsurplus] URM25

Paul,

AN/URM-25D was the first in a line that included AN/URM-25G, H, J & K.  J
and K are rare.  The signal generator used is the SG-85, which went through
four modifications, basic through D.  If you look on the signal generator
nameplate you should see a suffix letter after the 85, at least a "B".
NAVSHIPS 0967-187-5010 with 7 changes and 2 temporary changes covers 
AN/URM-25D, G
and H.  I have never found anything on J or K except a short calibration
instruction.  The power supply in AN/URM-25D is PP-977/URM-25D.  This 
changes
to PP-977A/URM-25G.  PP-977A has a 12 VAC winding and a regulator circuit 
for
the oscillator filament.  SG-85B is used in AN/URM-25H, and has the
outboard circuit board you found.  The circuit is a voltage 
double/regulator.  The
manual and changes do not make it clear whether the power supply went back
to PP-977, remained PP-977A either modified to remove the regulator or with
the regulator there but unused, or changed to PP-977B.  You might check that
out and report and I will add it to Change 7.  The added regulator circuit
and some rewiring associated with it were added with Change 7, but they did
not add a modified complete schematic.

One other comment - if the nameplate on your case still says AN/URM-25D but
the one on the signal generator says SG-85B/URM-25D or later, someone
swapped case or generator.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

n a message dated 10/12/2014 12:20:04 PM Central Daylight Time,
elespe at lisco.com writes:
> Got into a couple URM25D with an extra board mounted below the audio
> section behind the rf attenuator.
> Board has two power resistors, two electrolytics, two top hat diodes and a
> stud mount diode.
> I have not encountered this option before
> Can anyone enlighten me what it is?  Guessing maybe dc filament supply
> from size of components?
> I don’t find it documented anyplace I have looked
> Thanks
> Paul K0UYA
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