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RBZ Receiver
Portable miniature receiver · WWII

RBZ was a portable miniature valve-based receiver, introduced in 1943 by the Emerson Radio and Phonograph Corporation in News York (USA) for the US Navy. The receiver was used during Naval raids – for example during the D-Day landings – but also by resistance groups for the reception of BBC broadcasts. The device is powered by a battery pack and uses the helmet as its antenna.

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.
  
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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.
  
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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 [2] that British SAS troups used the RBZ Radio during Operation Houndsworth in Morvan (France) in June 1944 [3].

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
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The complete (unpacked) unit
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The complete set in the canvas carrying case
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The empty canvas carrying case
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Close-up of the frequency dial of the receiver
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Interior of the RBZ receiver
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Close-up of the dial
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Close-up of the valves
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Interior of the battery case
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Circuit diagram
Below is the circuit diagram of the RBZ receiver taken from page 55 of the instruction booklet [A]. 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.

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Checklist
  • CEX-46203
    Receiver
  • CEX-19040
    Battery pack
  • CEX-10172
    Base for receiver and battery pack
  • CZK-49216A
    Headphones assembly - 2 x Carron US-42 flat speaker
  • CVH-10204
    Skull cap for headphones (fits under M1 helmet)
  • CVH-10203
    Canvas carrying case
  • CEX-49238
    Helmet antenna lead-in
  1. CEX = Emerson Radio and Phonograph Corporation.

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
Documentation
  1. Instruction Book for Navy Model RBZ radio receiving equipment 1
    Emerson Radio & Phonograph Corp. New York, USA.
  1. Obtained from Tony (I0JX) [4].

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

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

  3. Wikipedia, Operation Houndsworth
    Retrieved November 2012.

  4. Tony (I0JX), The Navy RBZ receiver
    Retrieved October 2020.

  5. Kees Talen (K5BCQ), Bringing another RBZ back to life
    Retrieved September 2009.
Further information
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Crypto Museum. Created: Thursday 01 October 2009. Last changed: Saturday, 24 October 2020 - 09:36 CET.
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