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RBZ Receiver
The RZB receiver is a small self-contained army receiver with an external battery pack in a similar housing, that could be carried on the chest in a canvas case with two pockets. It was built in the USA around 1943 and was used for the reception of instructions and BBC broadcasts during WWII. It also played an important part during the British/US landings on the French coast after D-Day.

It was originally developed for the US Navy and was probably intended for the reception of instructions during beach landings. As such, both the receiver and the battery case are water tight and all accessories are cast in rubber. The two cases themselves are made from Bakelite.

The initial model had a frequency range of 2 - 5.8 MHz, but the unit was later modified for an extended frequency range of 5 - 13 MHz AM. The extended units were dropped over occupied European territory during WWII and were subsequently used by resistance groups.
  

As such, it resembles the British war-time MCR-1, the Sweetheart and the post war Mk-301 receivers. The RZB receiver was manufactured by the Emerson Radio and Phonograph Corporation in New York (USA) around 1943. The headset is connected to the battery case with a fixed rubber lead and consists of two flat speakers in a canvas skull cap, so that it could be worn under a standard helmet. Unfortunately, the skull cap is missing from the item shown here.

The receiver is beautifully built and operates around 5 valves: RF pre-amplifier (1T4), local oscillator/mixer (1R5), IF amplifier (1T4), detector (1S5) and the AF amplifier (1L4). For frequency adjustment it uses coil tuning (permeability tuning). The sensitivity of the receiver is 1 to 4 µV at 1mW audio output (into 600 ohm headphones).

The unit is powered by two voltages: 1.5V/250mA (LT) and 67.5V/4mA (HT). The rightmost picture below, shows the original batteries inside the battery compartment.
  

In Naval use, the soldier's metal helmet would be used as the antenna. A short piece of fixed wire (approx. 70 cm) and a screw-on terminal is used to connect the receiver to the helmet. Although it is uncertain whether these radios were issued to US Marines during WWII, it has now been confirmed [3] that British SAS troups used the RBZ Radio during Operation Houndsworth in Morvan (France) in June 1944 [4].

The complete (unpacked) unit The complete set in the canvas carrying case The empty canvas carrying case Close-up of the frequency dial of the receiver Interior of the RBZ receiver Close-up of the dial Close-up of the valves Interior of the battery case

Circuit diagram
Below is the circuit diagram of the RBZ receiver [1] taken from page 55 of the instruction booklet. Click the image to download the entire page in full resolution. Please note that the valves are drawn sideways, with the cathode on the left and the anode on the right.


Similar radios
The UK Type 36/1 (MCR-1) Norwegian Receiver Type 31/1 (Sweetheart) Polish OP-3 (Type 30/1) WW-II clandestine receiver Mk. 301 Receiver

References
  1. Emerson Radio & Phonograph Corporation,
    Instruction Book for Navy Model RBZ Radio Receiving Equipment.

    Contract number NXss-15891, Frequency Range 5-13 MC.

  2. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  3. Nobby Clark, Eye-witness account of a former SAS signals officer
    Private communication with Crypto Museum, November 2012.

  4. Wikipedia, Operation Houndsworth
    Retrieved November 2012.
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Crypto Museum. Last changed: Sunday, 16 August 2015 - 15:56 CET.
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