Widget Of The Week
General Radiological Ltd Type NE
Firemen often seem to have the best toys, which of
course are entirely necessary in their clearly hazardous profession, but who
amongst us wouldn’t want to have a ride on a fire engine or have a go with one of those
‘Jaws of Death’ car peelers? Fire station poles also look like a lot of fun and
how about a quick squirt with one of those high-power hoses? They’ve got loads
of more exotic stuff as well, and tucked away inside their equipment lockers quite a few of them have Geiger Counters.
This is not a new development in response to
any terrorist threats or atomic accidents, they’ve had access to them for decades, since
before the Cold War and for at least as long as there have been nuclear
weapons, power stations and radioactive waste being carted around the country.
Here’s an example of one that apparently they used to have back in the fifties
and sixties, at least that’s the story, which I have yet to corroborate, but it
all looks and sounds very plausible.
The age of this instrument, a Type NE 029-02 made by
General Radiological Ltd., is in little doubt though, and it proved fairly easy
to date. On the circuit board inside the case there’s a pair of TJ1 point
contact transistors and these were made by STC, but only for a brief period,
starting in 1956. I have Andrew Wylie and his excellent Mister Transistor
website to thank for that useful titbit and a wealth of other information about
vintage semiconductors. It’s a surprisingly compact design, most other military
and industrial Geiger Counters of the period tended to be large and bulky; this
one fits snugly in the palm of a hand.
It is really rugged, which fits in with the Fire
Brigade story; it’s almost certainly waterproof as well and easy to carry and
operate, even when the user is wearing thick protective clothing and gloves.
Inside the light but tough two-part cast alloy case there’s a Mullard MX129/01
Geiger Müller tube. This is mainly sensitive to Gamma Radiation, which can be
nasty stuff and is the kind that does the most damage and poses the greatest threat
to those unlucky enough to be close to an exposed source. On the top panel
there’s a small meter showing a relative reading of radiation dose in
milliroentgens per hour; the rotary switch below the meter has four positions:
Off, Battery Test and Sensitivity (0-0.5 and 0-5 mR/hr). Incidentally, nowadays
most instruments of this type measure gamma radiation dose in Sieverts and REMs
(Roentgens Equivalent Man), rather than mR/hr but the basic principle is the
same and if the needle moves, especially on the high range, you’ve found your
source radioactivity and it’s time to back off! The NE 029-02 also has an audio
output and comes supplied with a single headset, which plugs into a small
two-pin socket on the top panel. This allows the user to hear the clicks coming
from the detector tube, which can be helpful when trying to locate hazardous sources of radioactivity.
It is powered by three1.5 volt AA cells, which live
in a sealed compartment on the top panel. The two previously mentioned
transistors look as though they are used in a simple multivibrator circuit, which pumps
pulses of electricity into a coil and multiplier that generates the 400
or so volts needed to power the Geiger tube. As you may be able to see from the
photos it’s a real work of art, beautifully built, by hand, with all of the
components neatly soldered to orderly rows of pins. Fragile components, like
the point contact diodes have small coils wound into their leads to provide
some cushioning against knocks and bumps. Rubber seals around all of the case
and battery cover joints make sure water can’t get in.
I found this one hidden at the bottom of a pile of
Fire Brigade related items at a large open-air antique fair in Surrey. The
stallholder said the collection belonged to a retired fireman, and he believed
everything was standard service issue. It appeared to be in very good condition
and came with its original bright red carry case, shoulder strap and the high
impedance headset. The seller didn’t know if it was working or not, hence the
asking price of just £6, which I felt duty bound to haggle down to £4.00 –
bargain of the day!
Unsurprisingly it was as dead as a doornail and the
most serious fault wasn’t hard to find. A leaky set of cells had rotted away the
spring steel contacts in the battery compartment. Fortunately there was
no other damage and it cleaned up easily. Connecting a bench power supply
to the unit indicated that the battery test function was okay, but the detector
circuit remained stubbornly silent. The two transistors produced some slightly
anomalous readings but there were no obvious faults. Replacing the transistors
didn’t help so the suspicion has now shifted to the high voltage transformer,
half a dozen or so long obsolete selenium rectifiers and the Geiger tube. The
big problem, though, is the lack of a circuit diagram, so it will have to join
the waiting list until I have time to re-trace the circuit, or track down a
service manual. It almost certainly is repairable but it’s going to take time. On the plus side the condition, outside and in, is extraordinarily good;
the circuit boards looks as though they was assembled yesterday, and the case
shows only very light signs of use.
What Happened To It?
Up to date information on the sort of radiological monitoring equipment currently used by Fire Brigades in the UK is a bit thin on the ground but in 1995, in reply to a parliamentary question on the topic, it turned out that there were only 6 units to cover the whole of London. Seemingly radioactivity was not considered to be a huge priority back then. They’ve probably upped their game by now and it would be very surprising if a lot more instruments have not been issued, but it is highly unlikely that any of these old NE 029-02s are still in circulation.
General Radiological Ltd., was bought out by the Rank Organisation in the early sixties and since then seems to have vanished from sight. Although the NE 029-02 is well built
it is no match for modern instruments, in terms of sensitivity and accuracy, and my guess is
that they wouldn’t have remained in service for very long, probably less than 10 years.
Maintenance would have been a problem; first generation semiconductors had a
fairly short life expectancy Other components, like
electrolytic pacitors and selenium rectifiers, degrade over time and the one thing you don’t want
in a Geiger Counter, used in safety-critical applications, is unreliability.
can find no information on how many NE 029-02s were built but I suspect it was
probably in the low hundreds as the demand wouldn’t have been that great. That would make this one quite rare but sadly it doesn’t translate
into big bucks; it’s a bit too weird to attract most collectors of vintage
electronics, and unfortunately, in its present state it is of little practical
use. Nevertheless, it’s an unusual and arguably historical
example of early transistor technology and if anyone has any more information,
or a circuit diagram I would be very interested to hear from them.
First seen 1957
Original Price £?
Value Today £25
MX129/01 halogen-quenched gamma-sensitive Geiger Müller tube (0.0004 –
0.2R/hr), selectable range (0-5mR/hr & 0–0.5 mR/hr), 2 x transistor HV
generator (2 x STC TJ1), battery test function, waterproof case, headphone
output, carry case & strap supplied
Power req. 3
x 1.5 volt AA cells
x 123 x 49mm
Made (assembled) in: England
Hen's Teeth (10 rarest): 9