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Wire intercept receiver - this page is a stub

Lauschempfänger (intercept receiver) LE-40 was a sensitive audio amplifier used for covertly eaves­dropping on wired analogue telephone communications — also known as wire tapping — developed around 1940 by Algemeine Elektrizitäts-Gesellschaft (AEG), Kabelwerk Oberspree in Berlin-Oberschöneweide 1 (Germany). It was used by the German Army during WWII and was an improved version of its predecessor, the LE-35, with a built-in hum-filter. It was commonly used in combination with Lauschzange (current probe) LZ-35 which made it virtually undetectable [C].

The device is housed in a typical standard size panzerholz equipment case, as shown in the image on the right. The actual amplifier occupies the top 2/3 of the case, whilst the bottom half has various storage compartments for the LT/HT batteries, options, accessories and spare parts.

Like its predecessor, the LE-35, the amplifier of the LE-40 is built around three RV2 P800 valves that are accessible directly from the front panel for easy maintenance. A spare value is located in a socket at the top left of the bottom section.

Up to 8 lines can be connected simultaneously to the terminals on the left side. At the left of the front panel is a series of switches, eight of which are used to select the line that will be monitored.

The rest of the front panel holds an instrument (meter), a volume knob and a knob to select the required line impendance, between 40 and 5000 Ω. The device has a built-in 11-stage filter that removes any hum from the signal that is caused by the harmonics of the 50 Hz mains frequency.

Along the top edge of the front panel is the identification tag, which reveals the model (LE 40), the serial number (2818), the manufacturer (bxv) 2 and the year of manufacturing (1942). The the left of the identification tag is a stamp ("Ark.") to indicate that this device was suitable for use under arctic conditions. To the right of the tag is the Wehrmacht acceptance stamp (WaA. 584). 3

  1. The device featured here has manufacturing code (bxv), which was assigned to Algemeine Elektrizitäts-Gesellschaft, Kabelwerk Oberspree. The company was commonly known as AEG.
  2. According to [2], the code (bxv) was assigned to AEG, Kabelwerk Oberspree.
  3. WaA = Waffenamt (German Army Weapons Agency), tasked with overseeing Germany's rearmament process. Also tasked with and quality control and acceptance (Abnahme) of new equipment.  Wikipedia

Line selectors
Line impedance selector
Volume adjustment
Identification tag
Replacing a valve
Storage compartments for batteries and accessories
1 / 8
2 / 8
3 / 8
Line selectors
4 / 8
Line impedance selector
5 / 8
Volume adjustment
6 / 8
Identification tag
7 / 8
Replacing a valve
8 / 8
Storage compartments for batteries and accessories

Current probe   Lauschzange LZ-35
Lauschzange LZ-35 was a current probe that was mounted around a single wire of the analogue telephone line that had to be monitored, without galvanically touching it. This made the device virtually undetectable, as it did not affect the line in any way by causing a load or a disbalance.

The image on the right was taken from the LZ-35 manual [C], and shows the device intercepting an outdoor telephone line. The device was not small. It measured 120 × 70 × 60 mm and weighted 590 grams. At the bottom of the cylindrical enclosure are two screw terminals for connection to the Lauschempfänger, plus a strain relief ring for the amplifier wires.

Inside the device is a current transformer with a O-shaped core. Part of the core is hinged, to allow it to surround the wire that carries the audio. The transformer picks up the alternating magnetic field that surrounds the wire during a conversation, and feeds it to the amplifier.

The LZ-35 was originally supplied with the intercept amplifier LE-35, but also with the later LE-40. It was also used with the small and portable Drahtlauschempfänger D.L.E. (kl).

LZ-35 current probe. Image taken from the manual [B].

Complete kit
  • Intercept amplifier LE-40
  • Pair of headphones
  • HT battery
  • LT battery (accumulator)
  • Current probe (Lauschzange) LZ-35
  • Spare valve RV 2 P 800.
Technical specifications
  • Gain
    ~ 12 Neper (≈ 72dB) 1
  • Impedance
    40, 160, 600, 1600, 5000 Ω
  • Output
    15,000 Ω
  • Frequency
    150-2700 Hz
  • Filter
    11-stage for odd harmonics of 50 Hz
  • Valves
    3 x RV 2 P 800
  • Headphones
    Dfh. f 4000 Ω, or Dfh. a.
  • Dimensions
    461 x 361 x 260 mm
  • Weight
    36.5 kg
  1. 1 Neper ≈ 8.686 dB.

  1. Der Lauschempfänger 40
    Description and Instruction Manual (German).
    D 1068/1. 15 December 1942.

  2. Merkblatt zur Bedienung des Lauschempfängers 40, LE 40
    Operating instructions (German).
    D 1068/5. Berlin, 25 February 1942.

  3. Die Lauschzange LZ 35
    Current probe LZ-35 (German)
    D 1060/3. Berlin, 11 March 1938.
  1. Günter Hütter, Information about D.L.E. (kl)
    Retrieved July 2017. Photographed with kind permission.

  2. Liste der Fertigungskennzeichen für Waffen, Munition und Gerät
    Manufacturing codes for weapons, ammunition and equipment (German).
    Berlin 1944. Reprint 1977, Karl R. Pawlas.
Further information
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© Crypto Museum. Created: Wednesday 02 August 2017. Last changed: Saturday, 21 October 2017 - 15:05 CET.
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