Subminiature tube
A Subminiaturröhre or pencil tube is an extremely miniaturized Allglas- electron tube without base, together with the further miniaturized VHF - Nuvistoren represents the final stage of tube technology. The standard dimensions of the tube were 7 × 9 × 30 mm - the diameter of the glass tube roughly corresponds to that of a pencil , which is why the tiny tube type was also referred to as a pencil-valve or pencil-tube in the Anglo-American language area.
Military applications
As is so often the case with complex technical innovations (e.g. tension grid tubes , operational amplifiers ), the subminiature tubes were developed under the pressure of military superiority towards the end of World War II in the weapons electronics laboratories of the Allies, Great Britain and the USA . At the Applied Physics Laboratory of Johns Hopkins University in Baltimore , a team of scientists under the direction of its founder Merle Antony Tuve experimented on the construction of a novel, highly efficient proximity ignition electronics for anti-aircraft grenades , aerial bombs, and artillery and mortar projectiles . Due to the lack of space and the enormous forces (more than 20,000 g and approx. 30,000 / min) that occur when the grenade is fired and rotated, the electron tubes required for the technically demanding project had to be extremely miniaturized and their electrode system and the sensitive filament rigorously mechanically stabilized - In the case of subminiature tubes, the electrode connections are usually led to the outside via a squeeze-foot flat base and were connected directly to the circuit elements, the plug-in round base was rather the exception.
The electronic part of the first functional distance detonator was equipped with a subminiature triode ( oscillator ), two subminiature pentodes (amplifier stage) and a subminiature thyratron (switching tube).
After extensive research and experimentation, the breakthrough came in 1943: the simple impact fuses previously used were supplemented in the last two years of the war by intelligent, electronically controlled proximity fuses ( radio proximity fuze ), the functional principle of which was based on the Doppler effect . The proximity fuse, together with the radar and the nuclear weapon, is one of the most important military innovations of the Second World War - the effectiveness, accuracy and destructive potential of military explosive ammunition with electronic proximity fuels was first fired in 1943 in the Pacific War with those fired by the USS Helena (CL-50) and anti-aircraft grenades equipped with the new Mk 32 ignition device can be increased enormously. The new weapon played a decisive role for the Allies in the Battle of the Bulge . By the end of the war in 1945, with great effort and with the huge production capacity of the US electronics industry, more than 22 million proximity fuses had been supplied to the military.
Despite the availability of modern semiconductor elements, a large part of the analog avionics of the Soviet MiG-25 fighter jet , which was built until 1985, contained numerous subminiature tubes, whose resistance to a possible nuclear electromagnetic pulse NEMP ensured the functionality of the electronics and thus the combat readiness of the aircraft.
Civil applications
Until the invention of the transistor , particularly power-saving subminiature tubes were used as amplifier elements in small, battery-equipped electronic hearing aids . For example, the NF pentode DF651 developed for this is content with a heating voltage of 0.625 V at a heating current of 10 mA.
In 1954 the company brought Grundig the first miniaturized portable radio (Dimensions: 16 x 9 x 4 cm) called "Mini Boy" on the market: a powerful medium wave - superheterodyne , which was equipped with 4 subminiature. It remained the only commercial pocket radio from West German production with sub-miniature tubes, the competitors used the much larger socketed battery tubes of the D series with 1.4 V heating voltage. In the USA, the Motorola "Pixie" with similar dimensions was widely used. In addition to 4 sub-miniature tubes 1AH4, 1AJ5, 1AG4, this radio also had the tube 1R5 (= DK91) on board, a 7-pin miniature tube. Reception range: MW
The low-noise subminiature tubes for high-quality condenser microphones in professional studio technology such as B. the MSC2 from 1949 from the small company of Albert Hiller and the triode AC701 developed by Telefunken , which is used in the microphone models Telefunken Ela-M-251 , a relabeled version of the AKG C12 , in the Neumann Quadro or Stereo microphone QM69 / SM69 or was used in the M221 of the Schoeps company from 1954. The tiny tube made it possible for the first time to construct first-class microphones with a diameter of 20 mm.
Since there is no longer any production of sub -miniature tubes, common Noval miniature tubes such as the EF86 or the ECC83 work in the technically demanding impedance converter stages of current tube large-diaphragm condenser microphones .
The end of the electron tubes heralded the first commercial transistor radio in radio history that appeared on the US market and operated entirely with transistors in 1954 - but it took several years until the first West German fully transistor radios were ready for series production, and thus the end of the tube era, which was gradually becoming apparent .
literature
- Fritz Kunze, Erich Schwandt: Tube pocket table . 14th edition. Franzis, Poing 1994, ISBN 3-7723-5454-8 .
Web links
- Proximity fuse with sub-miniature tubes
- The Grundig Mini-Boy in the radio museum
- Applied Physics Laboratory, VR Radio Proximity Fuze (engl.)
- Patent specification Radio Proximity Fuze (engl.)
- History of the development of the distance fuse (PDF; 3.8 MB)
Individual evidence
- ^ Radio Proximity (VT) Fuzes , Department of the Navy - Naval Historical Center
- ↑ Video Grundig Miniboy 1954