The set has 4 x ARP12 RF pentodes and 1 x ATP4 OP pentode valves, two doing dual duty on transmit and receive. The receiver is a superhet with 285 khz IF, with the oscillator doubling for both modes. A reflex circuit is used on the final receive valve to amplify both IF and audio with a Westector diode detector. Power requirements are 3v and 150v DC. Click to see a circuit of the Mk II.
The Mk III (illustrated at right) was put into production in 1945 and internally was similar to earlier versions. The main changes were the introduction of a sealed aluminium case and a crystal calibrator bolted on externally (with an additional ARP12 valve). The calibrator plugs into the antenna socket when in use. The whole unit was carried on the wearer's back in a single webbing pack containing the battery with a mechanical remote control for On-off/Receive/Send.
Louis Meulstee has a good website with information on the WS38 as well as other British army radios.
Some hams have modified these sets for QRP CW use on 40 metres by switching the HT supply.
The original operating instructions for the Mk III were printed on two 8" x 5" metal plates and are probably not often seen. I have scanned these and you can access them below
Page 1 - gives instructions on setting up the station.
Page 2 - covers initial operating instructions.
Page 3 - explains calibration and netting.
Page 4 - shows a check list of the kit
The Mk III on the other hand has all its electrical connectors as well as headphones, mike and a short antenna. The external wiring to the calibrator was badly perished which seems to apply to most local examples so has been removed but retained. The direct battery connection to the set is still serviceable and is identical with B4 valve pins so a B4 holder makes a workable connection to external power. It is missing the webbing carry case. Click below for some pictures of my Mk III.
View 1 - interior of the Mk III
View 2 - another interior view
View 3 - the final interior shot
View 4 - calibrator No 9
View 5 - mike and phones combination set
View 6 - view with mike, phones, antenna and remote switch
Count since 1/7/07.
Page maintained by Simon Buxton VK2UA Created: 10/02/02 Updated: 14/1/2010