[Milsurplus] Stoddard PRM-1s (NM-20B) and PS

[Kenneth G. Gordon]

On 15 Feb 2016 at 15:34, Brian Harrison wrote:

> For sale - two Stoddard PRM-1s (NM-20B) with one PS and cable
> Both are working (one better than the other)
> Also one carrying case
> 
> All for $125 plus actual shipping
> 
> http://online.sfsu.edu/hl/src.html

For those who don't know, the NM-20B covers 150 kHz through 25 MHz, and 
has a BFO, so it can be easily used as an emergency or backup 
communications receiver.

In order for those receivers to work at top effectiveness, they need two 
easily-made battery packs mounted internally. I made mine using Radio 
Shack battery holders and standard C or D cells.

The receivers use all battery-tubes, and draw very little current. They are 
quite sensitive and stable, and are sufficiently selective for communications 
purposes.  

They have an excellent AGC circuit and a very large accurately calibrated 
signal strength meter. The manual for the civilian version is easily available 
on the web in PDF format. 

There are some differences between the NM-20B (civilian version) and the 
AN/PRM-1 (Navy version), mostly in the power supplies, although there are 
some minor differences in the receivers themselves.

I have two here, one of each kind, and one  of which I refurbished and use to 
track RFI and EMI, which was its original purpose. It has been very useful for 
this purpose, although it is heavy and somewhat complicated, and takes at 
least 30 minutes to setup and take down for each reading.

I usually run it from a small 75 watt inverter plugged into the car cigarette 
lighter socket.

I have rebuilt one of my Navy power supplies, by removing the selenium 
rectifier, and have added a Low Drop Out solid state regulator (for the DC 
filament voltage) and silicon diodes to mine.

I have all the accessories for at least one of my receivers, including the large, 
wooden tripods on which they were originally meant to be mounted, the 
remote meter, headphones, and large and small loops.

The two receivers offered via Brian include the original small loop antenna, 
and at least one includes the "sense" antenna.

Stoddart build and design-quality is really excellent. IMHO, Stoddart's 
equipment are real jewels.

If they were closer to me, I'd probably buy them.

I also have (given to me in an estate) models of Stoddart EMI/RFI "meters" 
which cover the frequency ranges from 8 kHz through 1000 MHz.

Ken W7EKB