Wireless of the Week - week 10

[Bruce Parker (RIP)]

Nothing is more typical of a British WW2 Tommy than his helmet worn on a cocky angle and a Wireless Set No.38 in its harness on his chest. It is arguably the most widely used and recognizable British/Commonwealth infantry set.

The 38 set is a lightweight portable radio designed for infantry work at the platoon or patrol level. Close to 200,000 sets were built by Mitcham Works (MW), Murphy Radio (MR) and Radio Gramophone Development (RGD) beginning in 1942 and were used in every theater by almost every Commonwealth country during WW2.

The 38 set featured is a Mk.2* version. Other versions include a Mk.1 which has the set and battery in one case, a Mk.III that is a sealed, tropicalized set and an AFV version modified for use in tanks.

The set itself is housed in a metal box 9” tall, 6-1/2” wide and 4” deep weighing 7 lbs. This was carried in a skeleton web harness with a web waist belt and a ring to attach to a brace attachment on the operator’s left web shoulder brace. The complete station with battery, headsets, spare valves, haversack, aerial bag and signals satchel weighed 22 lbs. The controls on the face of the set were simple to use and comprise of an off/receive/switch, a frequency dial with a lock and an aerial socket that had a rotating cover acting as a dust cover for whichever socket was not in use. A plug on a cable went from the set to a junction box carried in the haversack on the operator’s back. The headset and mic plugged into this box which itself had a short plug and socket that connected to the dry battery in the haversack. Aerials were 4’, 8’ or 12’ rod ‘F’ sections (as used on 19 sets) or a wire ground aerial. A dry battery carried in the haversack on the operator’s back provided 3 and 150 volts to the set. Alternatively, the set could be powered by a hand crank ‘Supply Unit No.5’. Included with the set was a card with operating instructions so, in theory, anyone could operate it if the real operator became incapacitated.

Frequency range was 7.3 to 9 megahertz. Operating range was approximately a half mile with a 4’ aerial and 2 miles with a 12’ one. The true frequency in ‘megacycles’ was shown in graduations on the dial which also tuned both the sender and receiver at the same time. The only other switch the operator had was a three position switch that was either off, receive or send. Sending required he use this switch as there was no pressel switch on the mic. The mic itself was novel in that it had two leather pads with the mic pickups inside them worn on the operator’s throat. His voice was therefore picked up…quietly…from his throat rather than his lips.

One of the most frustrating things with a 38 set is replacing a failed valve. The front cover comes off easily enough by removing the four screws in the corners. The valve replacement is typical and of no concern. It’s getting the screws back on where the trouble starts and can only be accomplished with a good magnetic screwdriver or a lot of skill and patience. Once complete you are asked to shellac the screws for waterproofing which, after several valve changes, makes a mess of the radio.