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Mini Corder E-120   TI-671/692
Miniature tape recorder

Mini Corder 120 was a body-wearable miniature tape-cassette recorder, made in the late 1970s in Czechoslovakia, probably by Tesla. 1 The device consists of an E-120 recorder and an U-120 play-back device, and was used in covert operations by the Czechoslovakian secret intelligence agency StB, the East-German Ministerium für Staatssicherheit (Stasi), the Polish Police 2 and by other intelligence services of the former Warsaw Pact countries. The recorder is also known by its codename ECHO and as project TI-671. Likewise, the player is known as URAL and as TI-692.
Although the set looks like a dictation device, or dictaphone, it has some characteristics that makes it more suitable for covert operations. It is built with first class electronic components and is housed in professional metal enclosures.

The miniature recorder is battery powered, but the batteries are housed in the remote control unit (RC), rather than in the device itself. This makes it easier to replace the batteries as the RC is usually carried in the hand. Both devices are marked with identification numbers (TI) of the Czechoslovakian Ministry of Internal Affairs.
E-120 Mini Corder and U-120 Transcriber

In order to minimise the size of the equipment, the smallest device is for recording only. It can not be used for playing back or winding the tape. As a result, it is small and lightweight, making it easier to conceal it on the body. The player is a desktop device that can be used for winding the tape and playing it back. It can not be used as a recorder. Judging from the date codes on some of the components, this unit was manufactured in 1977 or 1978. It is likely that several thousand units were made. According to surviving Stasi documents, it was no longer available in 1988 [2].
  1. Most of the components inside the devices are made by Tesla.
  2. The use of the Mini Corder 120 by the Polish Police is confirmed in a Power Point presentation about an exhibition with objects from the collection of the Polish Police Museum in Warsaw [1].

E-120 Mini Corder and U-120 Transcriber Components of the Mini Corder 120 E-120 Mini Corder with cassette U-120 Transcriber Spare tape cassettes Microphone Earphone close-up Inside the remote control unit

The diagram below gives a quick overview of the controls and connections on the two devices. The recorder has only two switches: one on the remote control unit, and one on the recorder's body. When a tape is in place and power is turned ON, it will start recording immediately.

Once recorded, the tapes can be played back in the large desktop player, or transcriber as it was called. It has a small control stick to (re)wind and playback the tape. Furthermore it has an optional speed control. The player is powered by internal batteries or by the supplied PSU.

E-120 Mini Corder   TI-671 - ECHO
The recorder measures just 84 x 65 x 18 mm and weights 174 grams. It is housed in a thin impressed eloxed aluminium enclosure with a professional look and feel. It is wired permanently to the microphone and to a black 2-pin male connector, to which the power should be applied.
The overall build quality suggests that it is not a consumer device. The batteries are not housed inside the recorder itself, but reside in a plastic remote control unit that measures 54 x 35 x 14 mm. Four thick button-type batteries are needed for a total of 6V. Power is controlled by means of a switch inside the remote control unit (RC).

In covert operations, the recorder is often hidden under the operative's clothing, whilst the RC is held in the hand with its cable running through the sleeve, or in another convenient place. This way, the recording can be started and stopped.
E-120 Mini Corder with cassette

A second RC is supplied to allow quick replacement of the batteries without the need to uncover the recorder. Sound is recorded onto a special tape cassette that is similar (but not identical) to a Philips Mini Cassette [4]. Before starting a recording session, the tape has to be erased, using the supplied eraser, and rewound to the beginning, using the rewind feature of the U-120 player.
Once the tape has been installed and the lid is closed, the recorder is enabled by sliding the switch on the recorder's right side to the ON position. This engages the tape transport system and places the tape before the recording head.

Once the RC is loaded with batteries and fitted to the black 2-pin plug, recording can be started by sliding the switch on top of the RC to towards the embossed dot. Sound is picked up by a small sensitive microphone, such as the one shown in the image on the right, that is wired permanently to the recorder via a thin grey shielded cable.

The tape can record 60 minutes of sound, after which it has to be turned over. A few spare cassettes were usually supplied with every set. Once the batteries were exhausted, they had to be replaced, either by swapping the RC for a freshly loaded one, or by opening it and replacing the button-type battery cells. A miniature screwsdriver was provided for opening and closing the RC.
E-120 Mini Corder Open recorder with tape Placing the tape Top view Right side with ON/OFF switch Front view - with model/serial number and lock Recorder with tape Tape head
Packaging Inside the packaging Contents of the package Remote control unit (battery holder) Holding the RC unit in the hand Microphone Miniature screwdriver E-120 Mini Corder with cassette

U-120 Transcriber   TI-692 - URAL
The player is housed in a strong metal enclosure, constructed from 2 mm thick eloxed aluminium panels. It measures 215 x 144 x 55 mm and weights 1.5 kg. The unit is powered by five 1.5V AA-size batteries, delivering a total of 7.5V (or 6V in case NiCd batteries are used). Alternatively, the player can be powered externally by the supplied PSU from the 120V or 220V AC mains network.
At the left is a small lid below which the tape cassette should be installed. The lid can be opened by pressing the recessed button at the left, after which the cassette can be entered. A small stick at the front edge is used to control the tape flow, shown here in the STOP position.

Before playing back a tape, it should be wound back to the beginning by pushing the stick to the left. To start play-back, push it towards the cassette. The recorded sound will be delivered through the built-in speaker at the right, and the volume can be adjusted with the rightmost knob.
U-120 Transcriber

As transcribing a conversion that has been covertly recorded with a concealed microphone can be difficult and requires a high level of concentration, it is possible to connect the supplied pair of stethoscope headphones to the SP/EAR socket at the right side. Entering a plug into this socket disables the internal speaker. The U-120 Transcriber is also known by StB designator TI-692.
U-120 Transcriber Front view Right Opening the cassette compartment Placing a tape cassette Battery compartment at the bottom Battery compartment Model and serial number
Packaging Inside the polystyrene packaging Mains transformer (6V DC output) Tape eraser Stethoscope headphones Earphone close-up Tape cassette seen from the top Tape guidance


Inside the packaging
Double sided tape cassettes Remote Control Unit (RC) and battery holder Microphone
Miniature screwdriver Earphones with stethoscope Mains Power Supply Unit for Transcriber
Tape eraser

Conversations are recorded onto a small cassette that measures 60 x 44 x 7 mm and that contains approx. 72 metres of ferro-magnetic tape. At a tape speed of 2 cm/s, this provides a recording time of one hour (60 minues) on each side of the tape. The total recording time is therefore 120 minutes, hence the names E-120 and U-120.

The width of the tape is 3.8 mm, which is exactly the same as that of the standard Philips Compact Cassette and the Mini Cassette of the era [3].
Tape cassette

The remote control unit (RC) is actually the recorder's power source and provides two functions. It can be opened with a miniature screwdriver that is also supplied. The RC has room for four cylindrical 1.5V button-type cells that should be installed as indicated by the (+) and (-) symbols. It delivers a total of 6V DC.

A small blue micro-switch controls the supply to the recorder. It is operated by a sliding knob on top of the RC, and can easily be operated with one hand.
Inside the remote control unit

A sensitive high-impedance microphone such as the one shown here, was supplied with each E-120 recorder. It was most likely manufactured by Sennheiser in West-Germany and was imported via clandestine channels. It was usually wired permanently to the body of the recorder by means of a a thin grey shielded cable.

In practice, small connectors were often inserted in the cable to make it easier to conceal the parts on the body, and to repair or replace the microphone if necessary.

Miniature screwdriver
This miniature screwdriver was supplied with each E-120 recorder in order to get access to the battery compartment inside the remote control unit.

It can also be used to get access to the interior of the recorder in case it needs cleaning or servicing, for example to replace the thin rubber driving belts.
Miniature screwdriver

Power supply
The U-120 player is usually powered by five internal NiCd batteries of 1.5V each, that provide a total of 7.5V. It can also be powered externally by connecting the supplied PSU to the DC 6V socket on the right side of the player.

The black circle on top of the PSU is the voltage caroussel, that allows selection between 220V and 120V AC mains networks.
PSU and plugs

Magnetic recording tape has to be fully erased before a new recording can be made properly. Normally, this is done in the recorder by means of a separate erase head that writes a high-frequency bias signal onto the tape.

In order to save space, power consumption and weight, the erase head has been omitted from the recorder. As the player has no facilities for erasing the tape either, an external tape eraser is supplied with the set. When pressing the black button, it provides a strong magnetic field that will erase any tape placed under it.
Tape eraser

Transcribing a covertly recorded conversation can be quite difficult and requires a high level of concentration. Audio can be played back via the player's internal speaker, or through the light-weight stethoscope earpiece shown in the image on the right, that was supplied with each set.

The earpiece is connected to the SP/EAR socket at the right side of the player. When inserted, the internal speaker is switched off automatically.
Stethoscope headphones

Spare tape cassettes Tape cassette Tape guidance Tape cassette seen from the top Side one Side two Remote control unit (battery holder) with start/top switch Remote control unit (battery holder)
Holding the RC unit in the hand Controlling the device Inside the remote control unit Battery compartment and start/stop switch Connectors Fitting the connectors Connectors fully seated Microphone
Miniature screwdriver Screwdriver compared to the size of a hand Earphone close-up Earpiece with cable Stethoscope headphones Mains transformer (6V DC output) PSU and plugs Tape eraser

The recorder is built on a strong metal frame that is housed inside a thin impressed eloxed aluminium enclosure that consists of two shells. The upper case shell is held in place by four miniature screws: two at the sides and two at the rear. Remove them to get access to the interior.
Inside the case is a sturdy enforced metal frame on which all mechanical parts are mounted. The electronic parts reside in the rear section of the unit and are kept to a minimum in order to save space, weight and energy. Most of the electronic parts are contained a rectangular metal cases.

The mechanics are actuated by a small electro­motor mounted at the rear right, that is made by Maxon in Switzerland. It drives a rubber belt that runs along the rear edge, which in turn drives the flywheel/capstan and, via another belt, the pick­up reel that is visible here at the front left.
Drive mechanics and electronics

When a tape is in place and the driving mechanism is engaged, the tape runs between the capstan and a rubber pressure roller, to the left of the recording head. Depending on the age and state, some of the rubber parts may have to be replaced after several years, in particular the belts. As ferro tape is used for the cassettes, it may be necessary to clean the recording head regularly. Note the disc with radial lines that is visible on the capstan/flywheel in the image above. It was used for adjusting the tape speed with a stroboscope, similar to the turntables of the same era.
Upper case shell removed Electronics Recording head detail Internal cover removed Interior - top view Drive mechanics and electronics Mechanics Interior

The player, or transcriber, is build on a heavy metal frame, housed inside strong metal enclosure, constructed from bended eloxed aluminium plate. The top half of the case is held in place by four large bolts: two at the front and two at the rear. After removing these four bolts and also the knobs on the control panel, the top half of the case can be removed and the interior is exposed.
All controls are mounted along the front edge of the metal frame, with the battery level meter at the center. The left side of the chassis carries the mechanical section, with the record head being the only electronic part. It is connected to the amplifier board at the right, which is mainly built with parts from the Tesla brand, which is why Tesla was most likely the manufacturer.

At the center of the frame, prominently visible in red, is the small electromotor that actuates the driving gear via a rubber belt. Like the one in the recorder, it is made by Maxon in Switzerland.
Mechanics detail

The image above shows the mechanism as seen from the left rear of the device. At the center of the screen are the pick-up and supply reels, the capstan, the pressure roller and the playback head. At the top left is the flywheel that is linked to the capstan via a rubber belt at the bottom.
The image on the right shows a bottom view of the metal chassis. At the bottom right is the battery compartment that has room for five 1.5V AA-size batteries. At the top right are volume and tone controls, speed adjustment and meter.

A small PCB is visible in the bottom left corner. It contains the motor driver and is connected to the Maxon motor and to the speed controls at the front panel. The circuit is factory calibrated to provide a constant tape speed of 2 cm/s, but can be adjusted manually by turning on SPEED CONTROL and setting the speed with the knob.
Bottom side

This can be useful if a tape has been recorded on a mis-aligned or worn-out recorder, or just to make it easier to transcribe a conversation, simply by slowing it down somewhat.
Player interior Top view with cassette lid open Flywheel Motor - made by Maxon in Switzerland Amplifier Mechanics detail Detail Bottom side

  • E-120
  • ECHO
  • TI-671
  • Mini Corder
  • U-120
  • URAL
  • TI-692
  • Transcriber
Technical specifications
  • Tape length
    72 m
  • Tape width
    3.8 mm
  • Tape speed
    2 cm/s
  • Recording
    60 min on each side
Help required
We are currently looking for additional information about the Mini Corder and Transcriber, such as a user manual, technical specifications and, if possible, a technical manual. Also information about the use of these devices is most welcome. If you have any information, please contact us.
  1. Institue of National Remembrance (Poland), Covert gadgets
    Power Point presentation with gadgets of the Polish Police Museum. Date unknown.

  2. Schiffel and Bauch, Strategie 2000, Elektronische Tonspeichertechnik
    GVS MfS 0201. Berlin, August 1988. MfS-Nr. B 46/88, page 3. BStU 000092.

  3. Wikipedia, Compact Cassette
    Retrieved March 2017.

  4. Wikipedia, Mini Cassette
    Retrieved March 2017.

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Crypto Museum. Created: Sunday 12 March 2017. Last changed: Friday, 07 April 2017 - 13:58 CET.
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