[Hallicrafters] Re: [Hammarlund] WTD URM 25 adaptors and cable(s)

[Roy Morgan]

On Jun 14, 2008, at 4:32 PM, rbethman wrote:

> Subject says it.
>
> Just had an AN/URM-25D delivered to me.  Fully lab checked.  has  
> about 4
> of the above mentioned items in the cover.  A whole LOT is missing.

There are only a couple you need:  the 50 0hm load for sure, and the  
one with the capacitor in it.

NOTES:

-Nolan Lee found he had to replace all the coax in one of these  
because it had become VERY lossy, especially at higher frequencies.
- The 50 ohm loads are available at fests: Tektronix and many others  
made them for use on scopes and other signal generators.
- You can make your own adapters:  a three inch piece of one-inch  
copper pipe, two end caps, two screws, and two BNC chassis mount  
connectors and you can mount whatever you need inside.
- WARNING!  if you have or get the one with the cap inside, replace  
the cap - it may well be leaky now and allow the B+ to leak in and  
ruin your attenuator.
- The Antenna Simulator (Dummy antenna) is nice but certainly not  
necessary for aligning the receivers whose manuals call for its use.   
The diagram for it is in the URM-25 manual.
- resistance checks at the output connector will tell you if your  
attenuator has been blown up by the above cause, or by some  
hammerfisted mechanic pushing the push to talk button on a transceiver  
while hooked up to the generator.  If  you find your attenuator fried,  
reply to me, I may well be setting up to fix them in about a month or  
so.  Odd resistors are needed of particular types and I may go to the  
trouble to source them.  (I have at least one blown attenuator here.)   
Look for equal dc resistance on all settings except the two end ones.

Lastly: do not live without a copy of the URM-25 Overhaul Notes from  
Hollow State news.  If your modulation does not work reliably or at  
all, you need to replace some caps in the Twin Tee network, also a  
number of other caps may well need to be replaced.  The Notes are on  
the web somewhere in PDF form.  (or I can send you a copy )

Roy


Roy Morgan
k1lky at earthlink.net
Lovettsville, VA 20180