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5-channel telephone tap
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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. It was
developed and built around 1941 by Deutsche Telephonwerke
und Kabelindustrie AG in Berlin (Germany) 1
and used by the German Army
during World War II.
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 .
According to ,
the manufacturer code (bxo) was assigned to Deutsche Telephonewerke
und Kabel­industrie. The company was located at Zeughofstraße 6-9,
Berlin SO-36 (Germany).
So far (2017) only three surviving units have surfaced.
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.
- Günter Hütter, Information about Verstärker 41
Retrieved June 2012. Photographed with kind permission.
- 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: Thursday, 28 December 2023 - 17:18 CET.