Tesla logo

As far as I know, there was only one manufacturer of semiconductor devices in the former sovereign state of Czechoslovakia: the Tesla company. The company used a number of logos, most involving the word Tesla plus a wave symbol, such as the one shown. On semiconductor devices, they used just the word TESLA in capitals.

I am indebted to a correspondent, Ivo, who provided me with fascinating information about Tesla. The company was formed in the years after the second world war by government directive. Research and development was based at the VUST Institute in Prague. (VUST stands for Výzkumný ústav sdělovací techniky, which means "Research Institute of Communication Technique"). The production was realized in the Tesla factory at Rožnov, a small Moravian town. In 1950, the experimental point-contact transistor was developed at VUST. Between 1953 and 1954, point-contact detector diodes and the development of alloy transistors was done. Production of the first PNP alloy transistors xNU40 started in 1955 followed in 1958 by production of the NPN alloy transistor series xxxNU70. In 1956, a demonstration transistor receiver was built with transistors xxxNU70, except for the oscillator, where the point-contact transistor was used because of its higher frequency. In 1958 a receiver "T58" was produced with transistors xxxNU70 as shown in this article.

Rather oddly, each Tesla NU transistor series is identified by its numeric suffix, and has a variable numeric prefix that denotes a maximum voltage characteristic.

As with all Eastern European semiconductor manufacturers, Tesla went through major changes after the fall of communism. Some of its parts still survive as specialist manufacturers.

wanted transistor I am very interested to find examples of Tesla's point-contact transistors type xNT40.

If you know anything about these, or have data about them, please

wanted transistor

I am also seeking examples of Tesla's point-contact diodes, which I believe are types 1NN40 - 6NN40 and 1NN41 - 7NN41. There is a page about these here.

If you know where I could obtain any, please

I am also very interested to find examples of Tesla's first junction transistors type xNU40 from 1955 in a flat black case. There may also have been a short series 1NU70 to 3NU70.

If you know where I could obtain any of these, or have data about them. please

wanted transistor

102NU70 transistor

Tesla's first production series of transistors is the xxxNU70 series of NPN AF low-power transistors (102NU70 shown):

  • 101NU70 - Vce 20 V, Ie 3 mA, 30 mW
  • 102NU70 - Vce 25 V, Ie 5 mA, 50 mW
  • 103NU70 - Vce 25 V, Ie 5 mA, 50 mW
  • 104NU70 - Vce 25 V, Ie 5 mA, 50 mW
  • 105NU70 - Vce 30 V, Ic 10 mA, 125 mW, h21e 20-40
  • 106NU70 - Vce 30 V, Ic 10 mA, 125 mW, h21e 30-75
  • 107NU70 - Vce 30 V, Ic 10 mA, 125 mW, h21e 65-130

There are also 'bílý' versions of 105NU70 to 107NU70 that have lower maximum collector voltage and slightly different gain banding. Google translates this word as 'white'. Ivo thinks that this denotes a white spot on the top of the case. This might be a way of selling devics that did not meet the full spec.

  • 105NU70 bílý - Vce 15 V, Ic 10 mA, 125 mW, h21e 20-45
  • 106NU70 bílý - Vce 15 V, Ic 10 mA, 125 mW, h21e 34-73
  • 107NU70 bílý - Vce 15 V, Ic 10 mA, 125 mW, h21e 68-120

The series 151-156NU70 are "high-frequency" ultra-thin base alloyed transistors used for AM receivers.

It seems that the early production of the xxxNU70 series, including these high-frequency types, used a flat black case like Tesla's first junction transistors type xNU40. I am very keen to find examples of these.

If you know about the flat can varieties, or can provide data for the high-frequency types, please

156NU70 transistor

There is also a series 101NU71 to 104NU71 of 250 mA types.

  • 101NU71 - Vce 30 V, Ic 250 mA, 125 mW, h21e 45-120
  • 102NU71 - Vce 30 V, Ic 250 mA, 125 mW, h21e 65-220
  • 103NU71 - Vce 48 V, Ic 250 mA, 125 mW, h21e 45-220
  • 104NU71 - Vce 20 V, Ic 250 mA, 125 mW, h21e 65-120

Tesla OC70 transistor

In the early 1960s, Tesla copied Western germanium junction transistors in the Mullard/Philips OC series. In my data books the only low-power ones listed are the OC169 (shown on the right ) and OC170, but I have found the OC70 shown on the left. Both are typical of most Tesla devices in having an imprinted decal, although later ones have direct printing on the metal.

Tesla OC169 transistor

GC transistors

Tesla also manufactured germanium types in TO-1A cans, apparently in various GDR-series, but using higher serial numbers, as shown by my example of a GS507 (germanium NPN RF low-power) in a plain metal can and a GC519 (germanium PNP AF low-power) in a black-painted one.

There are three series of PNP AF high-power transistors:

  • The NU72 series 2NU72 to 5NU72 are 4 Watt types in TO-66 cans, as shown. These are sometimes stated to be similar to the Mullard OC30, a version of which Tesla also made.
  • The NU73 series 2NU73 to 7NU73 are 12.5. Watt types in TO-3 cans. These are sometimes stated to be similar to the Mullard OC26 and OC27, versions of which Tesla also made.
  • The NU74 series 2NU74 to 7NU74 are 50 Watt types in TO-3 cans. Ivo informs me that these were used in the late 1970s as inverters in radio stations for ambulances, and with complementary GD6xx types in TVs.
4NU72 transistor

OA9 germanium diode

Tesla also made germanium diodes in the GA and GAZ series. The image on the right shows a GAZ51 in the ubiquitous TO-1A can; despite the Z this is not a Zener, it is a gold-bonded switching diode. They also copied the Philips/Mullard types OA5, OA7 and OA9 (shown on the left) although they did not copy the standard SO-2 glass tube.

GAZ51 germanium diode

4GAZ51 germanium diode

This unusual construction is the 4GAZ51, a set of four GAZ51 diodes for use in modulators / demodulators. The diodes themselves are unmarked except for some indistinct paint markings. I believe that there is also a 2GAZ51.

They also made silicon diodes in the KY and KYZ series. My image shows a KY701; it is not branded TESLA. Ivo informs me that these were made by Tesla Piešťany in Slovakia from 1967 onwards.

KY701 diode


Tesla also made germanium photodiodes:

  • 10PN41, 11PN41, 12PN41 and 13PN41
  • 10PN40
  • 10PP41, 11PP41 and 12PP41

I am looking for examples of all of these.

Tesla went on to make discrete silicon devices and integrated circuits, which I will not show here.

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