The type 955 triode "

acorn tube The 955 is typical of the acorn designs, named for the glass cap holding the terminals with the main part of the tube extending from it. An acorn tube, or acorn valve, refers to any member of a family of VHF/UHF vacuum tubes starting just before ...

" is a small

triode A triode is an electronic amplifier, amplifying vacuum tube (or ''thermionic valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated Electrical filament, filament or cathode, a control grid, grid ...

thermionic valve Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called ''thermions'' in early literature, ar ...

(

vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...

in USA) designed primarily to operate at high frequency. Although data books specify an upper limit of 400–600 MHz, some circuits may obtain gain up to about 900 MHz. Interelectrode

capacitance Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...

s and Miller capacitances are minimized by the small dimensions of the device and the widely separated pins. The connecting pins are placed around the periphery of the bulb and project radially outward: this maintains short internal leads with low

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the ...

, an important property allowing operation at high frequency. The pins fit a special socket fabricated as a ceramic ring in which the valve itself occupies the central space. The 955 was developed by

RCA RCA Corporation was a major American electronics company, which was founded in 1919 as the Radio Corporation of America. It was initially a patent pool, patent trust owned by General Electric (GE), Westinghouse Electric Corporation, Westinghou ...

and was commercially available in 1935. The 955 is one of about a dozen types of "acorn valve", so called because their size and shape is similar to the

acorn The acorn is the nut (fruit), nut of the oaks and their close relatives (genera ''Quercus'', ''Notholithocarpus'' and ''Lithocarpus'', in the family Fagaceae). It usually contains a seedling surrounded by two cotyledons (seedling leaves), en ...

(nut of the oak tree), introduced starting in 1935 and designed to work in the VHF range. The 954 and 956 types are sharp and remote cut-off pentodes, respectively, both also with indirect 6.3 V, 150 mA heaters. Types 957, 958 and 959 are for portable equipment and have 1.25 V NiCd battery heaters. The 957 is a medium-μ signal triode, the 958 is a transmitting triode with dual, paralleled filaments for increased emission, and the 959 is a sharp cut-off pentode like the 954. The 957 and 959 draw 50 mA heater current, the 958 twice as much. In 1942, the 958A with tightened emission specs was introduced after it turned out that 958s with excessively high emission kept working after the filament power was turned off, the filament still sufficiently heating on the anode current alone.{{cite web , url=http://www.antiquewireless.org/uploads/1/6/1/2/16129770/55-the_vacuum_tube.pdf , title= The Acorn Tube , author=Ludwell A. Sibley , access-date=2 April 2018

Pin connections

When viewing the device from above (the end without the exhaust tip), the pins are arranged in a group of three and a group of two, starting with the centre pin in the group of three and going in a clockwise direction, the pins are ''cathode, heater, grid, anode, heater''.

Ratings

The 955 is an ''indirectly heated triode'' with heater electrically isolated from the cathode. The heater has a 6.3 volt rating, which it shares with many other common thermionic valves/electron tubes, and it draws about 150 mA. The maximum anode voltage is 250 V, with an anode current of 420 microamperes and anode load 250 kilohm, and the maximum anode current is 4.5 mA at a voltage of 180 V with an anode load of 20 kilohm.Philips Valve Data Book, Philips Electrical Industries Pty. Ltd., 69-73 Clarence Street Sydney, Radio Valve Application Division, 1954. The 955 is designed to be used in the frequency range of 60–600 MHz (5-0.5 metres wavelength). The amplification factor obtained is between 20 and 25 depending on details of the specific stage design and operating voltage.

References

Products introduced in 1935 Vacuum tubes Acorns

Pin connections

Ratings

See also

References