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Tensor   Тензор
USSR spy radio set · 1942

Tensor 1 – sometimes written as Tenzor – was a spy radio set, developed in the USSR, and built by Silvania 2 near Moscow (Russia). It was introduced in 1942 and was used throughout WWII by the GRU and the NKVD, the forerunner of the KGB. After WWII, it was used by the GRU and the KGB, often as part of an (underground) cache for use before or during an invasion of Western Europe.

The set consists of four same-size aluminium units: transmitter, receiver, power supply unit (PSU) and filter, that can be connected together via cables, to form an operational radio station.

Except for the receiver, all valves are placed externally, which saves space and prevents the transmitter and PSU from overheating. All text on the bodies of the cases is in English, and all valves are American. This was clearly done to disguise its true identity. Furthermore it helped the GRU agents in operating the set, as many of them were foreign and did not speak Russian.
  
Tensor spy radio set

During WWII, most sets were kept in a canvas carrying bag, along with the valves and spare parts. During the Cold War, they were either supplied in a watertight metal container or in a wooden box. The image above shows the four main units of a Tensor Mark 2 that was probably produced in 1956. It is in remarkable good condition, with all of the cables still fully flexible and intact.

The four main units of the radio station are professionally made, with a keen eye for detail. Each unit measures 17.5 x 10.7 cm with rounded corners, and consists of a strong metal frame with removable lids at the top and at the bottom.

Each cover is strengthened by means of several embossed rigs and impressed windows, with clear engraved markings in the English language. Furthermore each unit is painted in two different colours (two-tone), which gives it a professional look and feel. The knobs are made of bakelite or – with the early version – machined aluminium.
  
Close-up of the transmitter

It is believed that Tensor was in production until the late 1950s. After WWII, the sets were mainly distributed by the GRU to agents (often in Western Europe) that could be activated in the event of a war. This is confirmed by the fact that quite a few Tensor sets were found after the Cold War, in caches in and around Vienna (Austria). The set featured here, was found in an attic in the former DDR 3 after the reunification of Germany. It had probably been kept there by a former GRU agent.

  1. In anatomy, the English word Tensor is used for a muscle that thightens or stretches part of the body. In Russian, the word Тензор is used for this.
  2. Slivania was and is a Russian valve (tube) manufacturer.
  3. DDR = East-Germany.  More

Wooden storage box Tensor spy radio set Complete Tensor setup with all units and accessories Filter unit PSU without valves Transmitter with crystal fitted (at the left) Receiver (RX) Morse key
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Wooden storage box
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Tensor spy radio set
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Complete Tensor setup with all units and accessories
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Filter unit
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PSU without valves
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Transmitter with crystal fitted (at the left)
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Receiver (RX)
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Morse key

Features
The diagram below shows all four units of the Tensor radio station, plus some of the accessories, ready for use. At the top centre is the mains filter unit that passes the mains voltage to the Power Supply Unit (PSU) at the centre of the diagram. A 9-position rotary switch is used for selecting the desired mains voltage. In most West-European countries it should be set to 240V. Three rectifier valves are fitted externally at the top surface of the PSU. The PSU provides the necessary voltages for the receiver (left) and the transmitter (right). The transmitter valves are also fitted externally.

Complete Tensor sentup with all units and accessories

The three receiver valves are fitted internally. The receiver delivers its audio directly to a pair of (supplied) headphones. A miniature morse key (visible at the front right) is connected directly to the transmitter. Also visible in the diagram are the separate wire antennas for the transmitter and the receiver, that allow full duplex operation. An external antenna tuning unit is provided to allow the antenna to be matched to the transmitter. More detailed information is provided below.


Versions
There are two known versions of the Tensor radio station:

  • Tensor Mark 1
    This is believed to be the initial version of the set, introduced in 1942. Its PSU has just two 5Z4 rectifying valves and the transmitter has two circular windows for reading off the frequency. Furthermore it is supplied with an older type morse key. The large knobs of the PSU's voltage selector and the transmitter's band selector are made of aluminium.

  • Tensor Mark 2
    From 1944 onwards, the PSU was given three 5Z4 rectifying valves and the transmitter had rectangular windows for reading off the frequency. It was supplied with a later type of morse key. The large selectors – and some other parts – are made of brown or black bakelite. It is believed that most Tensor units that were used during the Cold War, are of this type. The Tensor features on this page is a Mark 2 version that was made in 1956.


All parts of the Tensor radio station


Parts
Storage box
Box
Watertight cache container Canvas carrying bag
Bag
Power supply unit (PSU)
PSU
Mains filter unit Transmitter
TX
Receiver
RX
Morse key
Headphones Antennas Antenna matching unit Spare parts Maintenance and repair tools Operating instructions Transmission and reception schedule
Storage box
During the Cold War, the complete Tensor radio set was supplied in a wooden box that measures 41 x 28 x 16 cm and weights approx. 4.5 kg. Each part is individually packed in protective grease paper to allow it to be stored for an extended period of time.

The box was often hidden in a dry place such as an attic. Sets that were hidden in underground caches were usually packed in an hermetically sealed metal container, to protect it against moist, fungus, etc.
  
Wooden storage box

Cache container   wanted
When the Tensor set had to be stored in a moist place – usually as part of a secret underground cache – it was packed inside the watertight metal container shown in the image on the right.

The metal container shown here was found in the late 1990s in Vienna (Austria), when road works unexpectedly revealed a former Cold War USSR/Russian cache. Inside the container was a complete intact Tensor Mark 2 with accessories and operating instructions in German. It is now on display at the Austrian Signals Museum [3].
  
Cache storage container for Tensor

Canvas carrying bag   wanted
According to a wartime German publication of 1943, Tensor sets were commonly supplied in the canvas carrying bag shown in the image on the right [2]. The bag has several pockets for the accessories and spare parts. Alternatively, a strong leather bag was issued in some cases [5].

It is believed that this bag was not supplied with the Tensor radio sets that were issued during the Cold War, as these were stored for an extended period of time, without immediate action.
  
Canvas carrying bag, issued with Tensor during WWII [2]

Wooden storage box Storage case without the four units Accessories and spares Spare valves Slots for storing the units Cache storage container for Tensor Tensor accessories aside the cache container
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Wooden storage box
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Storage case without the four units
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Accessories and spares
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Spare valves
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Slots for storing the units
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Cache storage container for Tensor
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Tensor accessories aside the cache container
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Power supply unit   PSU
The Power Supply Unit (PSU) acts as the central hub to which all other units are connected. It has a fixed cable to which the mains voltage should be supplied, via the filter unit. The correct mains voltage should be selected with the large rotary knob at the front. At the top are three sockets in which the 5Z4 rectifying valves should be placed.

The PSU has two output sockets: one for the receiver (left) and one for the transmitter (right). The pins of these two sockets are different, so that the plugs can not be swapped accidentally.

  
Power supply unit (PSU)

Filter unit
The AC mains voltage is not supplied directly to the PSU, but via the filter unit shown in the image on the right. The unit has a fixed cable with a mains plug at the end, and a custom socket that accepts the PSU described above.

The filter unit contains four large electrolytic capacitors and some resistors, that are used for stabilisation of the DC voltages created by the PSU. As the capacitors are relatively large and do not fit inside the PSU, they are instead mounted inside the filter unit.

 View inside

  
Filter unit

Power supply unit (PSU) PSU without valves PSU left side AC mains voltage selector Power supply unit (PSU) PSU with large 5Z4 valves Transmitter power socket Receiver power socket
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Power supply unit (PSU)
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PSU without valves
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PSU left side
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AC mains voltage selector
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Power supply unit (PSU)
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PSU with large 5Z4 valves
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Transmitter power socket
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Receiver power socket




Transmitter   TX
The transmitter's power cord should be connected to the rightmost power socket of the PSU, which is marked 'TRANS.'. Furthermore, a morse key should be connected to the KEY socket at the right, and a suitable dipole antenna and counterpoise to the antenna sockets at the rear.

The transmitter can be adjusted freely by using the Variable Frequency Oscillator (VFO), but it is also possible to select the frequency by installing an appropriate crystal 1 in the XTAL socket at the left, as demonstrated in the image on the right.

At the top surface are two ceramic valve sockets: one for each transmitter stage. The leftmost one holds the metal 6F6 oscillator valve, whilst the large metal 6L6 PA-valve should be installed at the right. Each stage has its own frequency dial, which can be adjusted at the front edge, whilst the frequency is read from a window at the top.
  
Transmitter with crystal fitted (at the left)

The transmitter is suitable for the 3.7 to 14.3 MHz frequency range, divided over four bands (or ranges as they are called here) selectable with the large rotary knob at the right side. The selected range is visible in a rectangular window, just above the frequency readouts. At the rear edge are two indicator lamps that are used as an aid when tuning the transmitter stages. The leftmost one provides an indication of the oscillator activity. The rightmost lamp is used for tuning the antenna circuit or the amplifier stage (PA), selectable with a slide switch at the centre of the front edge. The transmitter has a power output of 13W or 30W, selectable with a toggle switch on the PSU.

  1. This is a unique feature of this transmitter, that is not commonly found on other spy radio sets of the era.

Transmitter (without valves) seen from the right Transmitter rear side Top view Transmitter with crystal fitted (at the left) Close up of range I frequency scale Band IV selected Band selector and morse key socket Crystal socket
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Transmitter (without valves) seen from the right
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Transmitter rear side
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Top view
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Transmitter with crystal fitted (at the left)
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Close up of range I frequency scale
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Band IV selected
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Band selector and morse key socket
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Crystal socket




Receiver   RX
The receiver is housed in a case that is very similar to that of the transmitter, but its valves are mounted internally. The receiver's power cord should be connected to the leftmost power socket of the PSU, which is marked REC. A suitable antenna and counterpoise should be connected to the terminals at the rear, whilst a pair of (supplied) headphones should be connected at the front.

The receiver's VFO can be adjusted freely over the entire 3.3 to 15 MHz frequency range, which is divided over two bands: 3.3 - 7 MHz (red) and 7 - 15 MHz (blue). Selecting the required band is not necessary as this is done auto­matically by an internal switch when turning the dial from the red to the blue section of the frequency scale.

With the wartime Tensor Mark 1, the receiver's circuit diagram was fitted on the top cover, in the large rectangular area behind the frequency scale. On the Mark 2 version — shown here — the diagram is omitted and the area is blank.
  
Receiver (RX)

Use the fine tuning knob at the front right corner to adjust the receiver to the desired frequency. It is also possible to use coarse tuning — available at both sides of the receiver — but the scale release knob at the front right has to be pressed whilst doing turning the coarse dial in order to prevent damage to the Pertinax dial that is driven by a small metal cogwheel (see interior below). At the front left corner is a knob that controls regeneration of the receiver and hence the volume.

Receiver (RX) Receiver (RX) Receiver rear side Controls and headphones socket Front view Close-up of the frequency scale Fine tuning the RX frequency Receiver power plug
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Receiver (RX)
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Receiver (RX)
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Receiver rear side
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Controls and headphones socket
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Front view
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Close-up of the frequency scale
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Fine tuning the RX frequency
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Receiver power plug

Morse key
A miniature morse key was supplied with the set, such as the one shown in the image on the right. Earlier Tensor versions may have been supplied with older model morse keys.

The morse key is connected to the two banana sockets at the right side of the transmitter, where the operator could also connect an alternative morse key.
  
Morse key

Headphones
The Tensor was supplied with a suitable pair of headphones, such as the one shown in the image on the right. It was made in the USSR and has caps made of synthetic rubber.

Other types of headphones are known to have been supplied as well.
  
Headphones

Antennas
Various wire antennas are supplied, each of which is wound onto a piece of wood, as shown in the image on the right. The transmit antenna has several taps, to allow it to be matched to the desired frequency band more accurately.

Seperate antennas and counterpoise wires are provided for transmitter and receiver, to allow full duplex operation (i.e. no switching of the antenna between transmitter and receiver).
  
Wire antennas

Antenna matcher
In order to match the antenna to the transmitter on a given frequency band, a small antenna tuning unit is provided. Three taps of the transmit antenna are connected to the tuner, whilst the tuner is connected to the antenna socket of the transmitter.

The exect operating procedure of the tuner is described in the manual.
  
Antenna tuner

Morse key Morse key interior Transmitter antenna Receiver antenna Counterpoise Ground wire Antenna tuner Tuning coil
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Morse key
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Morse key interior
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Transmitter antenna
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Receiver antenna
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Counterpoise
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Ground wire
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Antenna tuner
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Tuning coil

Spare parts
In order to allow for small repairs in the field, the set was supplied with a selection of spare parts, including:
  • Spare valves
  • Resistors
  • Capacitors
  • Light bulbs
  • Fuses
The image on the right shows some of the smaller spare parts as they were found with the Tensor featured here.  Full spares list

  
Spare parts

Tools
A selection of simple tools was supplied for carrying out basic maintenance and small field repairs. The image on the right shows the tools that were found with the Tensor featured here.

The large item with the wooden grip, is a soldering iron, that should be heated in a fire prior to use. Also supplied are solder, a piece of resin, a screwdriver and insulation tape.
  

Spare parts Spare parts Spare electrolytic capacitors Tip of the soldering iron Spare valves Spare valves Spare 6L6 valves
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Spare parts
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Spare parts
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Spare electrolytic capacitors
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Tip of the soldering iron
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Spare valves
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Spare valves
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Spare 6L6 valves

Operating instructions   wanted
Each Tensor station was supplied with brief operating instructions in the local language.

At present, no example of these operating instructions are available. You can help us expanding this page by providing a copy or a scan of the instructions, in whatever language.

 Contact us
  

Transmission schedule   wanted
Apart from the operating instructions, each set came with a personalized set of tables and instructions for the agent, for contacting the Russian Centre. These tables contain detailed transmission schedules for a given time, day, week and month, frequencies, call signs, etc.

The image on the right shows a single page of the transmission schedule for correspondent number 1742, as it was discovered in a Russian cache in Austria in 2007 [6].

 Download the schedule in PDF
  

The transmission schedule was supplied in printed form as well as on photo film, so that it could be hidden more easily and reproduced whenever necessary. The schedule consists of 1 page with global instruction and 10 pages with frequency, time and call sign tables. The schedule featured here was discoverd in 2007 and reproduced from the original film in 2017 by Eric Kelley [6].

  1. Instructions
    Anweizungen zur Arbeit
    Operating instructions

  2. Program (2 pages)
    Das Program der Verbindung des Korresp. Nr. 1742 mit dem Zentrum Nr. 2 oder Nr. 1
    Transmission schedule between Agent 1742 and Centre 2 or 1

  3. Tabelle Nr. 1
    Die Zeit der täglichen Arbeit des Korresp. Nr. 1742 mit dem Zentrum Nr. 2 oder 1
    Time table for days of the month between Agent 1742 and Centre 2 or 1

  4. Tabelle Nr. 2
    Arbeitsfrequenzen für tägl. Arbeit des Korresp. Nr. 1742 m. Zentrum 2
    Frequencies for daily operation of Agent 1742 with Centre 2

  5. Tabelle Nr. 3
    Arbeitsfrequenzen für tägl. Arbeit des Korresp. Nr. 1742 mit Zentrum 1
    Frequencies for daily operation of Agent 1742 with Centre 1

  6. Tabelle Nr. 4
    Rufzeichen und Koeffiziente des Korr. Nr. 1742, des Zentrums 2 oder 1
    Call signs and check numbers for a given time of the day and month

  7. Tabelle Nr. 5 (3 pages)
    Funkunterlagen für die Arbeit auf Kontroll-freq. des Korr. Nr. 1742 mit Zentrum 2 od. 1
    Information for operating on check frequencies

  8. Tabelle Nr. 6
    Einseitige Lehrsendungen mit Tonschwankungen
    Unidirectional exercise transmissions with tone fading
All text is in German, which means it was intended for a German-speaking agent. If you look carefully at the second page of the Program (2), you can faintly see some Russian text bleeding through the page, which suggests that the film was prepared in Russia. In the text, the word correspondent is used for the agent, whilst the Russian base station is identified as Centre.

 Download the complete transmission schedule in PDF


Interior
The main parts of the Tensor spy radio set are housed in four similar metal enclosures that hold the transmitter, the receiver, the power supply unit (PSU) and a mains filter unit. The cases are made of light metal alloy, of which the shapes have been pressed. The cases are painted in two tones of grey, with white engraved lettering. Each case consists of a body and two lids: one at the top and one at the bottom. The serial number of each unit is engraved on the exterior of the bottom and the interior of each lid. The sections below describe the interior of each unit.

Transmitter
The transmitter is housed in a metal case that measures 17.5 x 10.5 x 4.8 cm (without the valves) and weights approx. 1100 grams when the valves are fitted. It has two removable lids: one at the top and one at the bottom, each of which is held in place by four recessed screws along the edge.

Remove the screws from both sides and remove the two covers. This will expose the transmitter's interior. The image on the right shows the upper section that holds the two frequency scales (each with the four ranges printed in distinct colours), the band selector, with the same colours, two indicator lamps and the two valves sockets.

The bottom side contains the tuned circuits and the passive components. At the centre are the large coils of the PA and antenna sections. At the right is the oscillator in a separately shielded section, with the oscillator coil at the centre.
  
Transmitter interior top view

The unit is extremely well-built with a keen eye for the smallest detail. All parts are identified by numbers that correspond to the circuit diagram.

Transmitter interior (top) Transmitter bottom section. Note the isolated cut-out in the cover. Transmitter interior bottom view Top view Bottom view Oscillator coil PA coil and antenna coil Band selector
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Transmitter interior (top)
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Transmitter bottom section. Note the isolated cut-out in the cover.
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Transmitter interior bottom view
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Top view
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Bottom view
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Oscillator coil
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PA coil and antenna coil
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Band selector

Receiver
The receiver is housed in a metal case that measures 17.5 x 10.5 x 4.7 cm and weights approx. 936 grams. It has two removable lids: one at the top (held in place by three recessed screws) and one at the bottom (held in place by three large bolts). Remove them to get access to the interior.

Actually, the user normally only needs to have access to the bottom section, as that is where the three 6J7 valves are located. In order to remove the valves, the Pertinax cover panel below the antenna terminals has to be removed first. It is held in place by two black screws.

The image on the right shows the interior of the receiver, as seen from the top. The frequency dial is prominently visible at the left and covers most of the circuits underneath. The dial is made of Pertinax and is actually a big cogwheel, that is driven by a smaller one on the fine tuning knob.
  
Receiver interior top view

The frequency dial has a red and a blue half, each representing one of the two frequency bands that are supported by the receiver. A small switch, hidden under the dial, automatically selects the appropriate band when turning the dial from the red to the blue section. The band selector switch is visible through a hole in the dial and is driven by a notched disc on the dial axis.

Tensor receiver circuit diagram. Source: Wireless for the Warrior, Volume 4 [1].

The receiver is built around three identical 6J7 valves that form the RF, detector and audio stages. It is currently the only unit of which the circuit diagram is known [1]. In order to remove the three 6J7 valves, the small cover panel near the antenna terminals has to be removed first.

Receiver interior (bottom) Receiver interior top view Receiver interior bottom view Top view Bottom view Three 6J7 valves inside the receiver Fine tuning cogwheel (made of Pertinax) Auto range sensing switch
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Receiver interior (bottom)
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Receiver interior top view
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Receiver interior bottom view
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Top view
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Bottom view
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Three 6J7 valves inside the receiver
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Fine tuning cogwheel (made of Pertinax)
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Auto range sensing switch

Power supply unit   PSU
The PSU is housed in a metal case that is similar to that of the transmitter and receiver. It has the same length and width, but is somewhat higher in order to accomodate the large AC transformer. The case has a lid at the top and bottom, each of which is held in place by four recessed screws.

The interior of the PSU can be accessed by removing both covers. About half the available space is taken by the mains transformer, which is tightly fitted between the sides of the case.

The remaining half — visible in the image on the right — holds the sockets for the three rectifying valves, the power selector, the indicator lamps and the remaining passive components. Note that a neon lamp is used to indicate the selected HT voltage and, hence, the transmitter's power output (which can be either 13 or 30 Watts), depending on the position of the VOLT switch.
  
Valve sockets and indicator lamps

A remarkable feature of this PSU is the absense of any (electrolytic) capacitors for stabilisation of the DC voltages. These capacitors are present but are located inside the separate filter unit – that is connected between the PSU and the AC mains – probably because of their dimensions.

PSU interior upper side Valve sockets and indicator lamps PSU interior bottom side Top view Resistor and wiring detail Wiring detail Neon lamp (HT voltage) Wiring detail
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PSU interior upper side
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Valve sockets and indicator lamps
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PSU interior bottom side
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Top view
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Resistor and wiring detail
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Wiring detail
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Neon lamp (HT voltage)
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Wiring detail

Filter unit
The filter unit has the same dimensions as the transmitter and the receiver, and weights 765 grams. Although it is a separate unit that is connected between the mains and the Power Supply Unit (PSU), it is actually an integral part of the PSU, as it contains the electrolytic capacitors (and some resistors) that are needed for stabilisation of the various DC voltages provided by the PSU.

For this reason the filter unit has a 6-pin socket to which the PSU is connected. Two pins of this connector provide the mains AC voltage directly to the PSU, whilst the other lines bring the DC voltages provided by the transformer and the rectifying valves inside the PSU back to the filter.

At the time the Tensor set was produced, the quality and life cycle of electrolytic capacitors was largely unknown and unpredictable. For this reason, a set of replacement capacitors was supplied with the kit. With the supplied soldering iron, the operator was able to do a field repair.
  
Filter unit interior

All four electrolytic capacitors are specified at 20µF. Although their quality is unpredictable, the ones in the device shown above still have a capacity of 17µF, which is well within their original specification. Capacitors of this aga have to be rejuvenated from time to time (see below).

Filter unit interior Filter unit interior seen from the top Electrolytic capacitor Resistors Filter unit contact panel Filter unit resistor detail
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Filter unit interior
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Filter unit interior seen from the top
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Electrolytic capacitor
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Resistors
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Filter unit contact panel
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Filter unit resistor detail

Restoration
The Tensor spy radio set featured above was in mint condition when it was rediscovered, which means no restoration of the exterior was necessary. Furthermore all movable parts (switches, dials, etc.) were still freely movable and all cables were soft (i.e. not rigid and brittle) and intact.

The storage box had clearly seen some action and, although it is not a critical part of the set, the wood had dried out somewhat and some panels had come loose. Furthermore, the bottom padding had fully desintegrated and was sticking to the parts inside the box. For these reasons we decided to take the box partly apart, repair any cracks, glue the parts back together and give the inside of the box an invisible protective layer.

The padding was replaced by contemporary felt, in order to protect the equipment, accessories and the spare parts when stored inside the box.
  
Slots for storing the units

The image above shows the restored box with the spare parts stored inside, and the four units removed. When testing the radio, we first connected it to the mains by means of a VARIAC, and gradually raised the voltage from 50V to 230V in small increments, over the course of an hour.

This was done to protect and rejuvenate the electrolytic capacitors of the Filter Unit. Once the reformation cycle was over, the transmitter and receiver were connected to the PSU and tested.

The transmitter worked straight away, both with and without a crystal. It could easily be tuned to the connected wire antenna, using the indicator lamps on the body of the transmitter. Next, the receiver was tested. It worked straight away, but appeared to be insensitive. Furthermore, it was impossible to correctly adjust the regeneration control, resulting in interfering audio tones.
  
Three glass 5Z4 valves on the power supply unit

After measuring the HT voltage supplied to the receiver, it was noticed that this was down at 70V, which is not enough to properly drive the 6J7 valves, for which the nominal voltage should be in the 100V range. After checking the 5Z4 rectifier valves on the PSU, it turned out that one of them was not functioning properly. After swapping it, the HT voltage increased to 97V and like magic the receiver worked as expected. The Tensor featured on this page is now fully operational again.

Storage case without the four units Accessories and spares Spare valves Slots for storing the units Three glass 5Z4 valves on the power supply unit
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Storage case without the four units
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Accessories and spares
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Spare valves
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Slots for storing the units
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Three glass 5Z4 valves on the power supply unit

Connections
The PSU acts as the main hub that connects all units of the Tensor radio station together. It has two custom power sockets for the receiver and the transmitter, plus a fixed cable with the custom 6-pin plug at the end, that connects to the filter unit. The pinout of each socket is given below.

Transmitter power
  1. 0V (common)
  2. LT 6.3V AC
  3. HT1 low: +300V DC, high: 400V DC
  4. HT2 low: +500V DC, high: 650V DC
Receiver power
  1. 0V (common)
  2. LT 6.3V AC
  3. HT 97V DC
Filter unit
The filter unit is a rather strange device and should be considered an integral part of the PSU. It passes the mains voltage (in our case 240V AC) to the PSU (via pins 4 and 5) and contains the electrolytic capacitors for stabilisation of the various DC voltages of the PSU, simply because they do not fit inside the PSU. The PSU generates two high voltages: +300V and -300V, which are connected in series to provide 600V for the transmitter. As a result, the transmitter and receiver do not share the same 0V rail. Furthermore, one side of the mains is connected to the virtual 0V.

  1. DC +97V
  2. DC +275V
  3. DC +325V
  4. 0V (common, virtual)
  5. AC 220V (mains)
  6. DC -318V
Technical specifications
Transmitter
  • Power
    13-30W (CW only)
  • Frequency
    3.7 - 14.3 MHz
  • Ranges
    4  see below
  • Valves
    6F6, 6L6
  • Size
    17.5 x 10.5 x 4.6 cm (without valves)
  • Weight
    1000 grams (1106 grams with valves)
Ranges
  1. Red
    3.7 - 5.2 MHz
  2. Black
    5.2 - 7.2 MHz
  3. Green
    7.2 - 10.2 MHz
  4. Yellow
    10.2 - 14.3 MHz
Receiver
  • Frequency
    3.3 - 15 MHz
  • Ranges
    2 (automatically selected by dial)
  • Valves
    3 x 6J7
  • Size
    17.5 x 10.5 x 4.6 cm (without valves)
  • Weight
    639 grams
PSU
  • AC mains
    90, 100, 110, 125, 140, 180, 200, 220 and 240V
  • Size
    17.5 x 10.5 x 6.1 cm (without valves)
  • Weight
    3080 grams (with valves)
Filter unit
  • Size
    17.5 x 10.5 x 4.5 cm (without valves)
  • Weight
    765 grams
Valves   tubes
  1. Two or three rectifier valves, depending on model.

Spares
  • 3 x Electrolytic capacitor 20µF.
  • 5 x Light bulb 2V/75mA, E10 fitting
  • 1 x Neon lamp
  • 2 x Resistor 100 kΩ/2W
  • 1 x Resistor 1 kΩ/1W
  • 1 x Capacitor (?)
  • 4 x Fuse 1A
  • 4 x Fuse 2A
Documentation
  1. Transmission schedules and instructions for correspondent 1742 (German)
    Created in 1939 and supplied on paper and film. Discovered in an Austrian cache in 2007. Reproduced from film by Eric Kelley in 2017 [6].
References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  2. Hauptamt Ordnungspolizei, Funkpeilung der Kurzen Wellen, 1. Teil
    Berlin 1943. pp. 164-165.

  3. Austrian Signals Museum, Tensor in watertight metal cache container
    Photographed July 2015.

  4. Military Historical Collection - Gausdal, Image of Tensor Mark 1
    Website. Retrieved October 2017.

  5. User 'Luger', Russian spy radio 'Tensor'
    War Relics Forum. Retrieved October 2016.

  6. Eric Kelley, Tensor transmission schedule 1742
    USSR, 1939. Discovered 2007. Reproduced from film 2017.
Further information
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Crypto Museum. Created: Sunday 15 October 2017. Last changed: Saturday, 16 December 2017 - 11:20 CET.
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