Just picked one up, any pointers on restoration would be appreciated.
Pinout on the power jack would also be appreciated. Plug # would also be
appreciated. Battery replacement etc.

Many thanks

Ray

On Dec 3 2007, 12:40*pm, wrote:
Just picked one up, *any pointers on restoration would be appreciated.
Pinout on the power jack would also be appreciated. * Plug # would also be
appreciated. *Battery replacement *etc.

Many thanks

Ray

Ray,

Regarding the NM-25T: I'm pretty familiar with this unit. I have
three of them, a complete set of antennas and a manual. The three pin
power connector on the front a two for 120 VAC and one for chassis
ground. With the unit sitting in the upright position - meter facing
towards you, the bottom pin is the ground or green wire and the other
two are 120 VAC. The resistance across the two pins for 120 VAC
should be around 175 Ohms or so with the power switch on or in the
charge position. The resistance to ground should be in the megs. Be
sure and check it with an Ohmmeter since it's possible the plug has
gotten rotated. I picked up a matching connector at APEX Electronics
in Sun Valley California just above Los Angeles. They're a common
connector originally made by Cannon.

Batteries. The unit takes 12 C-size Ni Cad batteries. They are
inside a gasketed box in the uper left side of the receiver - inside
of course. Removing the battery compartment is easy. There is a two
pin plug on a short grey cable. You need to push in on a wrap around
type spring that secures the connector. Generally, the place to push
is on the side of the plug facing the front panel. Simply push in on
the spring with a small screwdriver and the plug should easily pull
out from the battery box. Then remove the two long screws with the
round heads. They go all the way through the battery box and into the
bracket. Once you have the battery compartment free there are four or
six flat head screws you need to remove. Once they are removed you
will need to gently pry the lid off. I had my battery pack rebuilt at
Batteries Plus at the cost of about $90.00. With a good set of
batteries but low, the battery meter in the upper left should read
about 12-14 Volts when charging begins. When charging is complete it
should read about 16 Volts or so. This is an expanded meter scale.
The receiver actually operates on 12 Volts from an internnal
regulator. It takes about 8 hours or longer to fully charge a set of
good batteries. The current drain from the receiver is pretty low so
a good set of freshly charged batteries should run the receiver about
40 hours continuous.

The switches in the receiver may also need to be cleaned. I use a
Caig supper-dupper gold contact spray. The tuner assembly, accesible
by removing 80 bazillion screws, is similar to a standard coil tuner
type assembly. If you need to clean the contacts I would suggest a
piece of t-shirt with the Supper-Dupper spray on the cloth and wipe
the contacts on the turret assembly - not the spring contacts. Do not
use anything abrasive like a pencil eraser as this will take the
plating off.

You will find that this is an excellent piece of test equipment as
well as a great receiver. The meter is calibrated in Volts as well as
dB relative to 1 uV so a meter reading of -20 would be 0.1 uV and +20
would be 10 uV. You get the idea. The input impedance is 50 Ohms and
to make actual field intensity meter reading you need a calibrated
antenna with a known antenna factor. For relative readings you don't
need anything fance but you should have a matching unit to match
whatever pickup device you are using to the 50 Ohm input. Without that
it will gve some strange readings as far as amplitude tracking over
any appreciable range goes. When you put it in the CAL postion
youshould hear, after a few seconds, a tone that sounds like about a
600 Hz squarewave. This is normal and the gain is typically set to
read about 30-35, but you need to determine that with a calibrated
source. I primarily use mine as a bridge detector when making antenna
measurmeents.

I hope this gives you a starting point. If you have any further
questions please feel free to contact me.

Burt, K6OQK