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Verstärker 41
5-channel telephone tap - this page is a stub

Verstärker 41 (amplifier 41) was a multi-channel audio amplifier, used for eavesdropping on up to five analogue telephone lines simultaneously — also known as wire tapping — and recording the intercepted audio, developed and built around 1941 by Deutsche Telephonwerke und Kabel­industrie AG in Berlin (Germany) 1 for use by the German Army during World War Two (WWII).

The device is housed in a so-called panzerholz enclosure with a removable lid at the front. Behind the lid is the control panel, that holds the selectors, adjustments and all connections.

Central to the system are 5 analogue telephone line interfaces, implemented as removable plug-in modules. The lower half of each plug-in unit holds the adjustments, whereas the upper half contains the thermionic valves (tubes). In normal use, the upper half of the plug-ins is covered by a hinged lid, as shown in the image on the right.

Each plug-in also holds a so-called magic eye indicator, that is visible through one of the five holes in the hinged lid. At the top right are the multi-way sockets to which the telephone lines are connected. At the bottom are two rows of toggle switches. The green switches are used to connect one of the telephone lines to the head­phones. The red switches are used to determine which line will be recorded to one of the two tape recorders that can be connected externally.

To improve operation of the device in a dark and improvised environment, a standard Wehrmacht work lamp can be installed at the top. Although Verstarker 41 may have been used to intercept suspected (enemy) lines, it was mainly used to monitor the telephone lines of citizens and high-ranking German officers. It is believed that only a small quantity of Verstärker 41 units was made, as only three 2 of them have surfaced so far. The device shown here as serial number 164 and was built in 1943. Many thanks to Günter Hütter for allowing us to photograph the unit [1].

  1. According to [2], the manufacturer code (bxo) was assigned to Deutsche Telephonewerke und Kabel­industrie. The company was located at Zeughofstraße 6-9, Berlin SO-36 (Germany).
  2. So far (2017) only three surviving units have surfaced.

Front panel Front view with cover raised Verstärker 41 in horizontal position Valves Controls Perspective view of Verstärker 41 Removing one of the plug-ins One of the plugs-in removed from Verstärker 41
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Front panel
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Front view with cover raised
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Verstärker 41 in horizontal position
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Perspective view of Verstärker 41
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Removing one of the plug-ins
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One of the plugs-in removed from Verstärker 41

The diagram below shows the location of the various controls and connections at the front panel of Verstärker 41. At the top left is the socket to which the mains AC supply is connected. The correct AC mains voltage should be selected with the caroussel at the lower left. Sockets for two independent headphone circuits — marked I and II — are available at the bottom left and right.

In practice, the magic eye would indicate that a line was in use. The green switches are then used to connect one of the headphone circuits (I or II) to that line. Likewise, one of the two recording circuits (also marked I and II) can be connected to the line by means of the read switches along the bottom edge. Lines and tape recorders are connected to the 33-pin sockets at the top right.

At present, no further information about Verstärker 41 is available. We are looking for any documentation of this device, such as brochures, descriptions, technical documentation, mention of the device in litarature, etc. If you can provide any of these, please contact us.

  1. Günter Hütter, Information about Verstärker 41
    Retrieved June 2012. 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.
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© Crypto Museum. Created: Thursday 31 August 2017. Last changed: Saturday, 21 October 2017 - 14:08 CET.
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