rd  - 1962 - ENC Conference

DARTMOUTH COLLEGE
~EPART.~IEXT OF OHE~ISTR~"
HANOVER • NEW HAMPSHIRE
Insert Construction for Nl~ Probe
io Place the coax fitting and the insert tube (note i) in the jig.
2. Wind uninsulated, oxygen free~ high conductivity copper wire
(OFHC, 30 gauge) around the tube° Space the turns with fine
thread and secure the ends under tension from rubber bands. (note 2)
3. Warm the tube to about 60 ° and apply a very thin layer of epoxy
resin (note 5) so that it flows evenly around wires and thread.
~. Heat briefly (about 2 minutes) at IOO ° until the resin is tacky,
remove the thread and apply a second coat of resin~ using the
minimum amount to get a uniform coating. Bake at iOO ° for
thirty minutes°
~o Bend the free ends of the wire~ slightly separated, down to the
coax fitting9 secure with Scotch Tape~ coat with resin and bake.
6. Trim one lead to just reach the "dimple" depression and solder
with a minimum amount of solder and heat.
7. Remove from the jig, bend the second lead smoothly under the
bottom of the insert to the center, and then do~mo Trim short so
that when the tip of wire is inserted into the pin jack and the
parts are assembled, there is no excess wire and it lies smoothly
in the groove without touching the metal case of the coax plug.
Solder the lead to the pin jack and assemble°
8° Coat the bottom of the insert tube with epoxy resin (note %),
press the tube into the coax plug and place the assembly in the
jig. Remove excess resin to give a smooth joint and bake until
the resin has set°
Note s o
i. Clean the insert tube with trisodium phosphate solution, water,
aqua regis, water and then ammonia, in turn, and bake to dry.
2o For proper balancing, the coil should be tipped very slighly
rather than being exactly perpendicular to the axis of the tube.
The wire can be obtained from various sources, one of which is
Sigmund Cohn~ 12~ S. Columbus~ Mt. Vernon, N.Y.
3. Ciba Araldite Resin 6010 cured with hardener Araldite HN-9~I,
available from Do Ho Litter Co.~ Inc., PO Box 247, 30 Lowell
Junction Road, Ballardvale~ Mass.
4. Any commercial resin with a non-metallic loading, such as Hysol
or One-Ton etc. The Ciba resin might work but it is claimed that
the addition of an inert filler improves dimensional stability
over a wide range of temperature change.
8-1-61 Paul R. Shafer