[R-390] SG-25

[Jim Amos]

I bought a URM-25 C at Dayton in which the modulator didn't work.  It also
turned out to be one of the paper capacitors.  After replacing the cap,
everything worked great.  It was one of the ones that was part of the
oscillator function, and not a coupling capacitor.

73's 
Jim N8CAH



-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Bernice & Al
Sent: Monday, June 07, 2004 9:45 PM
To: r-390 at mailman.qth.net
Subject: [R-390] SG-25

Purchased a SG-25 Signal Generator last weekend at a local Hamfest for $15
CDN. Asking price was $20, offered 15 and he took it. Should have offered
10. I bought it with the intentions of removing the main tuning capacitor to
use in a crystal radio. Fair Radio sold them at one time for this purpose.
The capacitor is a high quality part, ideal for high performance crystal
radio. When I opened up the unit I just did not have the heart to part out
such high quality  piece of test equipment.

The generator is in good condition. It operates well. O/P seems to be within
spec for frequency and level. All functions work. The only problem is that
after about 45 minutes of operation all modulation is lost. Could be the
paper caps will change them out. I have a URM-25F which had a similar
problem. After changing the caps the problem was still there. It finally
turned out to be the meter diode. Found this by touching the diode lead with
a hot glass rod. The modulation dropped out within a second or so. Replaced
the diode and the generator has been working for about 4 years now.

I have number of questions about this unit.

1: What is the history.What are the differences, if any with AN/URM-25...?
The unit is sure nice inside. Very clean but will be a problem if some caps
down in the innards have to be replaced. The ID Tag has this printed on it.

                            Trad
        STANDARD SIGNAL GENERATOR

       MODEL SG-25        SERIAL NO. 544
 TRAD ELECTRONICS CORP. ASBURY PARK N.J.

2: From what I can find out this is civilian version of the AN/URM-25,
version C, D, I don't know?

3: Is there a WWW site with URM-25 history.

4: The front panel is not painted. The aluminium finish appears to be either
a "silver" anodize or a clear chemical film. Similar to araldite. I would
like to refinish the panel. Either redo in the original finish or paint.

5: The case is painted grey, about the same colour as the URM-25F. It is
stencilled with "AN-URM-25-D". Is this the norm.

6: The signal Generator came with these accessories.

    1: IMPEDANCE ADAPTOR
        MX-1487/URM-25D

    2: IMPEDANCE ADAPTOR
        MX-1487/URM-25D
        PART OF AN/URM-25H

    3: TEST LEAD
        CX-1363/U
        PART OF AN/URM-25H

    4: ANTENNA SIMULATOR
        SM-35/URM-25D
        PART OF AN/URM-25H

    5: CG-409/U ( 0' 5')
        (Have 2 of these. They are original with the aluminium cable marker.
RG-58C/U coax.)

Comments and advice on any repair or refurbishment would be appreciated. I
also need information on the reliability of paper caps in the metal tube,
with the one end soldered to the case for the ground connection.

I have requested in with W.J. Ford Surplus here in Canada to rent, for
thirty days, a manual. If I can't get one and any one out there needs any of
the extra accessories maybe a trade could be arranged or trade for a missing
accessory.

That's it for now. Hope I didn't bore anybody.

Al


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