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EDI CIA FBI Alpha One → ← M-60 ← UMY-25
The M-75B and its predecessor M-60 are based on
the UMY-25, which was developed for the
US Central Intelligence Agency (CIA),
and was introduced in 1962. Being a secret device,
the name of the manufacturer (EDI) was not printed on the case. In 1966/67,
the CIA switched to the more advanced Nagra SN which
had been secretly developed for the US
intelligence and law enforcement community
by the Swiss firm Nagra Kudelski.
As a result, EDI was able to release the UMY-25 on the commercial market,
and with a few modifications this became the M-60/M-75B.
It was officially marketed as a pocket memo recorder — i.e. a dictation
machine —
but was in reality aimed at private investigators, law enforcement agencies, and
foreign intelligence services.
In 1971, the M-75B was succeeded by the Alpha One, which was no longer
manufactured by EDI, but by Amerex Electronics Inc. for Identcorporation
in Japan. The Alpha One is very similar to the M-75B, but has a modernised
interior and uses a tape cartridge instead of open reels.
The accessories of all models (UMY-25, M-60,
M-75B and Alpha One) are interchangeable.
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Differences with the UMY-25
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Compared with the original UMY-25 recorder of the CIA,
the following differences are observed:
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- Manufacturer brand name (edi) on case lid
- Brushed aluminium case rather than brown/beige
- No fixed (hard-wired) start/stop switch
- Different IC packaging: WC183T (TO-5) instead of WC183G (flat-pack) [a][b]
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Advantages over earlier devices
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Compared with earlier devices from other manufacturers, such as the
Mohawk series and the Protona Minifon,
the M-75B had the following advantages:
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- Small
- Lightweight
- Low power consumption
- Stereo
- Quiet
- Simple operation
- Auto-stop
- Stabilised speed
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- No flywheel
- Non-standard tape width
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The table below shows an overview of minature tape recorders that are
clearly related, based on the observations of collector JBond
on the jwsoundgroup forum [3].
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Below is the circuit diagram of the M-75B, based on the diagram published by
[2]. At the left is the stereo record/playback head (H1/H2), followed by
two amplifiers (IC1, IC2); one for each channel. Each amplifier is built
around a WD183T [a][b], which is one the first integrated circuits
(ICs) developed by Westinghouse (USA) for use in miniature hearing aids.
The amplifiers are used for recording as well as playback by routing the
inputs and outputs via the accessory socket.
The circuit is powered by a single 1.4V mercury battery cell (B1) of which
the (+) terminal is also routed via the accessory socket.
At the right is the
motor circuit which is powered by a separate 1.4V mercury battery cell (B1). The
motor is enabled by transistor (T1) as soon as the main power is applied (B1).
At the end of each magnetic tape is a piece of conducting tape that shorts
the contacts of the auto-stop switch (SW1). It cuts the power to the motor
(M1) and stops the tape.
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At the right side of the device is an 11-pin socket for connection
of the microphone, speakers, start/stop switch etc. This SRM11S socket
is made by JAE (Japan) and accepts an SRM11P plug. Compatible plugs
were made by Winchester and CDM Electronics.
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- Head 1
- GND
- Head 2
- Out 1
- GND
- Out 2
- In 2
- not connected
- In 1
- Battery 2 (+1.4V)
- Power input (+1.4V)
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Below is the wiring of the accessory connector when recording the audio from
the two connected microphones: MIC1 and MIC2. Note the three wire loops in the
connector: AD, BE and CF. A switch should be connected between contacts L
and M. It connects the battery (B2) to the circuit.
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Below is the wiring of the accessory connector when playing back audio via the
two speakers or headphones: SPK1 and SPK2. Note the three wiring loops in the
connector: AK, BE and CH. A switch or a loop wire should be connected between
contacts L and M to enable the power.
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Device Miniature covert body recorder Purpose Covert recording and evidence gathering Format Open reel magnetic tape Manufacturer Electro Data Inc. (EDI) Model M-75B Year 1967 Country USA Predecessor M-60, UMY-25 Successor Alpha One (Amerex) Channels 2 (stereo) Power 2 × 1.4V Mercury Cell Dimensions 130 × 72 × 25 mm Weight 225 g Price US$ 585 (est.) 1
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Price estimation based on the B-60 models, announced in July 1967 in [5].
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692 Crypto Museum, Netherlands 955 Vintage-Technics, Russia
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© Crypto Museum. Created: Tuesday 12 March 2024. Last changed: Saturday, 17 May 2025 - 16:32 CET.
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