[Milsurplus] AN/URM25-J

[Mark Richards]

Robert,

Thanks so much for your help on this.  The schematic is especially clear.

I have some progress to report.  The 25D unit does work.  I had the 
front panel controls incorrectly set!

The other does not, and it's suggested that the filament regulator is 
not needed in a fixed installation anyway, so I will simply wire around it.

Both units are otherwise in very good shape and I think at least the 25D 
is worth restoring.

We'll see how that does.

73,

/Mark
K1MGY



On 12/04/2013 17:28, WA5CAB at cs.com wrote:
> Here's an extracted schematic (permission is not granted to put this 
> on BAMA).  I added a couple of notes that aren't actually on the 
> complete hard copy of the manual that I sell.  The power supply used 
> with the original SG-85 is PP-977.  You have a poor copy of the 
> schematic for that.  As you can see, the power transformer T-201 only 
> has two windings.  With SG-85A the power supply changed to PP-977A and 
> T-201 has three windings.  The third one is 12 VAC and there is a 
> regulator built into the power supply for the VFO and Xtal oscillator 
> tubes.  The SG-85B also used PP-977A but the page added with Change 6 
> (AN/URM-25H) says that the supply to the new regulator board is taken 
> from point H which is the filament supply to the rest of the tubes in 
> the set, which would imply that the third winding isn't used.  I 
> actually have an SG-85B but it's over in storage because I've been 
> using an SG-85A (AN/URM-25G).  One of these days I'll drag it home and 
> find out.
>
> The SG-85C is supposed to use a PP-6601/URM-25J.  What's different 
> about it I don't know.  One possibility is that they removed the third 
> winding, but if that's all, they should have called it PP-977.
>
> In a message dated 12/04/2013 12:55:57 PM Central Standard Time, 
> mark.richards at massmicro.com writes:
>> On 12/04/2013 01:25, WA5CAB at cs.com wrote:
>> >And the SG-85B/URM-25D used in AN/URM-25H has an oscillator
>> >filament regulator board added that is not in the first two 
>> versions.  The two
>> >diodes are 1N540's.  The two capacitors are 2200 uf 10 VDCW.  The two
>> >resistors are 15 ohm 5W.  And the zener is a 1N3998A 6.2V.  Probably 
>> the same
>> >board.
>> That's exactly this board!  You must have a schematic that's better than
>> my URM25D schematic.  But I looked at BAMA and there's nothing for a
>> URM-25H.
>>
>> /k1mgy
>
>
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480