[R-390] Differences between the various URM-25 generators?

[Craig C. Heaton]

Tom,

I've been meaning to reply for the past couple of days. As Roger, AI4NI, has
mentioned, there were many flavors.

When I purchased my R-390/A, a URM-25D with manuals came with the deal.
First glance the identification plate on the front panel give the typical
information, SG***** what ever; AN/URM-25D. The plate on the cabinet gives
more information; URM-25G. Both list the same serial number!

And to add to the confusion; reading the manuals there is mention of a
Oscillator Filament Regulator Assembly (AN/URM-25H only). My 25D has this
board, so at some point it has been upgraded to the H version. This board is
connected to the filament of V101 (6AH6).

So, maybe someone working in one of the repair depots at this time period
could give a little insight.

More info: Beg, borrow, or steal a copy of Dallas Lankford's notes on
recapping the URM-25D. While looking at a scope connected to my 25D the
modulated waveform left room for improvement. the top of the waveform was
fine, bottom of the waveform wasn't modulated the same (less) and distorted.
After recapping life was good. Well worth the money spent and I think this
sig-gen is ready for another 50 years, can't say the same about my HP 8640B.

73's
wd8kdg
Craig



-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Tom Norris
Sent: Tuesday, November 28, 2006 3:02 PM
To: r-390 at mailman.qth.net
Subject: [R-390] Differences between the various URM-25 generators?


I've seen the "F" model with the flat panel, and I have a Trad SG-25
with a brushed metal front but otherwise appears to be identical to
the "B".  The one manual I downloaded from LOGSA ages ago "says" it's
for the URM-25B, but the unit in the manual bears little resemblance
other than general circuit description.  What other variations were
there?

73

Tom NU4G


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