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TI-462 A   PLUTO
Spy radio receiver

The TI-462A was a small valve-based Short Wave (SW) receiver, developed and built in 1956 in the former Czechoslovakia by Správa 6 1 for use by the secret state police (StB) and by Správa 1 (espionage). The receiver was initially designed as part of the PLUTO spy radio station, but was also used stand-alone. A modified variant was used with the later SIRIUS spy radio set.
The TI-462 was a very compact and lightweight receiver. Despite the fact that it contains 11 valves (tubes), it measures only 19 x 10 x 5 cm and weight just 1.27 kg. Most components were manufactured by Tesla, but the valves came from Valvo and Raytheon 2 . Its physical appearance is similar to the receiver of the American RS-6 set.

When it was used as part of a spy radio set, the TI-462 was usually powered by the transmitter. It was also supplied for stand-alone use however, in which case it came with its own power supply unit (PSU) or external battery.
PLUTO receiver (TI-462A)

The TI-462 A was developed in 1956 and was released the same year as part of the three-piece PLUTO spy radio set. It was used in international espionage, mainly in West European countries. Although the set came with a small morse key that was mounted inside the accessory box, the receiver had a built-in automatic morse keyer with a removable paddle at the front right. The keyer was connected to the transmitter via the 6-pin 270° DIN connector at the rear right.

A modified version of the TI-562 A was supplied in 1962 with the SIRIUS I spy radio set. The differences with its predecessor were the modified frequency range and the omission of the automatic morse keyer, as the SIRIUS set came with a complementary high-speed morse burst encoder. Apart from engraving the new frequencies, the enclosure was left unchanged, which accounts for the three unused holes at the front right corner of the device shown above.
  1. Správa 6 refers to Government Department 6: Communication Technology.
  2. Although Valvo and Raytheon were European and American manufacturers, who would normally not supply a country behind the Iron Curtain, some Eastern Block countries, like Hungary and Czechoslovakia, often managed to get Western components anyway, by ordering them via a neutral country like Austria.

PLUTO receiver (TI-462A) PLUTO receiver (TI-462A) PLUTO receiver (TI-462A) Top view Frequency scale Adjustments Frequency tuning dial Fine tuning

The image below shows the PLUTO receiver as seen from the rear right corner. A 6-pin DIN plug is used to connect it to the transmitter from which it gets its power. If necessarry, a simple morse key can be connected to the two banana sockets at the right. Alternatively, on the TI-462 only, a plastic paddle can be mounted at the front right in order to use the built-in automatic morse keyer. Two crystal earphones can be connected to the sockets just above the morse key sockets.

PLUTO receiver (TI-462) controls and connections. Click for close-up.

As the receiver was commonly used for the reception of morse signals (CW), a Beat Frequency Oscillator (BFO) is present in order to produce an audible tone. It can be enabled with a slide-switch at the front edge. The desired frequency range is selected with the band swich and the frequency can be adjusted with the large tuning ring at the side. Fine tuning is possible with the VENIER dial. The frequency scale can be calibrated by means of the built-in calibrator at the front.
Top view Right side Frequency scale Adjustments Frequency tuning dial Fine tuning Frequency range selector

There are at least two different versions of the TI-462 A receiver, but it is not possible to determine the variant from the serial number. It is likely that existing receivers were later modified for newer requirements. The following versions are currently known:
  • Mark I
    The initial 1956 version of the receiver had two frequency ranges: 2-4 MHz (range 1) and 4-8 MHz (range 2). Furthermore, this version had a built-in automatic morse keyer (also known as an elbug keyer) with a plastic paddle sticking out at the front right corner.

  • Mark II
    In 1962, the TI-462 A was also supplied with the SIRIUS spy radio set. The two frequency ranges were modified: (1) 4-8 MHz and (2) 8-16 MHz, and the new figures were engraved in the enclosure aside the range switch. Furthermore, the automatic morse keyer was omitted as the SIRIUS set came with the DÁVAČ high-speed morse burst encoder. It is very likely that existing PLUTO receivers were modified this way.

Automatic morse keyer
Although a morse key is normally not part of a receiver, the TI-462A was equipped with a built-in automatic morse keyer that allowed the operator to send dashes and dots at higher speed. It is connected to the transmitter via the 6-pin DIN plug at the right and was probably built into the receiver for convenience of operation. In addition, a normal morse key can be connected as well.
The image on the right shows the interior of the earlier version of the TI-462A which has a built-in keyer. A transparent plastic paddle, which is usually stored in the accessory box, can be inserted into a hole at the front of the case and can be fixed with a plastic screw at the centre.

By moving the paddle left and right, a series of dots and dashes is produced. The speed can be adjusted with the SPEED knob at the front edge of the receiver. When the receiver is put back in storage, the plastic paddle was usually removed first and stored in the accessory box again.
Operating the automatic keyer

The automatic keyer, and hence the plastic paddle, were similar to the PIVONKA keyer that was issued separately as a universal keyer for various spy radio sets. It was also supplied as a backup keyer for radios that already had a built-in one or that were supplied with a morse burst encoder.
Manual morse key
A small morse key was supplied with the radio set as a backup, for example in case the auto-keyer was out of order, or when the operator was not trained on the use of the automatic keyer.

The key was mounted inside the accessory box from within it could be operated, and was connected to the right side of the receiver by means of two banana plugs. The morse key operates a relay inside the receiver that in turn switches the HT voltage of the transmitter. The arm of the key can be collapsed sideways.
Morse key

Plastic paddle Mounting the plastic paddle Screwing the paddle into place Operating the automatic keyer Morse key Simple morse key connected directly to the receiver

PLUTO spy radio set
The TI-462A was initially developed in 1956 as part of the PLUTO spy radio set, that consisted of a transmitter, a receiver and a metal box with the accessories. The receiver was powered by the mains power supply unit of the transmitter.

At present, we only have the receiver in our collection and are still looking for the transmitter and the accessory box.

 More information

SIRIUS spy radio set
The TI-462A was also supplied with the SIRIUS spy radio set, that was introduced in 1962. The SIRIUS transmitter was much more powerful than the PLUTO transmitter (80W rather than 12W), making it easier to cover a 2000 km range.

Furthermore, the SIRIUS set was supplied with a high-speed morse burst transmitter, making it less prone to radio direction finding.

 More information
Complete SIRIUS spy radio station


TI-462A exterior and interior side-by-side

The TI-462 A is housed in a grey hammerite-painted metal enclosure that consists of two case shells that are held together by a couple of screws at the bottom. After removing the bottom shell, the interior can be taken out of the top shell, as shown in the image of the receiver above.
Two variants of the PLUTO receiver are known to exist. They are both shown in the image on the right. The one on the left is the initial TI-462A that was supplied as part of the PLUTO radio station in 1956. It is built on a pertinax base panel and has a built-in automatic morse keyer.

The one on the right is the later TI-462A that was supplied in 1962 with the SIRIUS spy radio station. It is built on an epoxy base panel and is missing the automatic morse keyer, which is the reason for the empty space at the front right corner. If necessary, the keyer can still be fitted.
TI-462 (left) and TI-462A (right)

All controls and active components (i.e. the valves) are mounted at the upper side of the unit, on the pertinax or epoxy panel. All passive components are mounted at the compartmented bottom side. The tuning elements of the HF and IF stages are all at one side of the frame, so that they can be accessed for alignment through a removable panel in the bottom of the metal enclosure.
TI-462A (PLUTO) exterior and interior TI-462A interior TI-462 (left) and TI-462A (right) TI-462 interior Components detail Valves detail Interior detail Controls and automatic morse keyer
Mounting the plastic paddle Operating the automatic keyer Bottom view Bottom view Close-up of the IF strip with the crystal filters Pre-amplifier and 1st IF stage components Interior detail Tuning capacitor

Block diagram
Below is the simplified block diagram of the TI-462 A. It is a superheterodyne receiver with two frequency ranges. The desired frequency can be adjusted with a variable frequency oscillator (VFO). A crystal filter in the IF section makes the receiver suitable for the reception of narrowband CW signals (morse), and a beat frequency oscillator (BFO) is used to make the CW tones audible.

At the bottom is the morse keyer, which is not actually part of the receiver but was probably placed here for convenience. It consists of two parts: a conventional morse keyer section at the right, suitable for driving the HT voltage of the transmitter, and an automatic morse keyer on the left. The latter part was omitted from the later TI-462A. When operating the keyer, the receiver is disabled and an audio tone is injected into the earphone circuit for monitoring (side-tone).
  1. KEY (-)
  2. 175V AC (HT)
  3. 0V AC
  4. 6.3V AC (LT)
  5. GND
  6. KEY (+)
  1. PLUTO Technical Manual (without circuit diagrams)
    1956 (page 1 missing, scanned from original faded document).

  2. PLUTO circuit diagrams
    1956 (scanned from original faded document).

  1. Anonymous, PLUTO receiver - THANKS!
    Device and documentation kindly donated by anonymous former user. July 2015.

  2. Louis Meulstee, Wireless for the Warrior, Part 4 Supplement
    Forthcoming. Accessed August 2015.

Further information

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Crypto Museum. Created: Friday 31 July 2015. Last changed: Friday, 22 July 2016 - 14:09 CET.
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