Identify It! answer for 12-08-2009

Another round of great guesses. The answer to this Identify It! Challenge is:

Identify It! for 12-08-2009

Identify It! for 12-08-2009

These items are Nuvistors. Nuvistors are the smallest mass produced vacuum tubes and were invented and produced by RCA for use mostly in consumer electronics. Nuvistor is a play on words including “Nu” which sounds like “new” and vistor which sounds like the end of transistor. “Nu” is also similar to “Mu” which is a symbol which stands for the amplification factor of a vacuum tube.

Unlike most vacuum tubes Nuvistors are enclosed inside a metal shell that both provides structure and shields the elements inside the tubes from radio frequency interference. Being metal they are a little more rugged than glass tubes, although unlike transistors they are prone to problems due to vibration. Nuvistors are unique in their manufacture in that instead of each tube being evacuated of air individually and then sealed, entire sets of tubes were placed into a large vacuum chamber, the air removed from the chamber, and then each tube sealed roboticly before all tubes were removed from the chamber. Being small reduced weight and due to the physical smallness of the elements within the tube (cathodes, grids, plates) Nuvisors worked well with high frequency (such as VHF and UHF frequencies used in television transmission.)

Like all tubes, Nuvistors contained a heater, cathode, at least one grid, and a plate. The heater was a wire made of tungsten which is not unlike a filament in a light bulb. Electricity passing through the filament to glow and produce heat. This heat is transferred to the cathode a metal sleave that is wrapped around the filament (but not electrically connected to it). The Edison Effect (noted by Thomas Edison) is that any metal heated in a vacuum will release a charge of electrons into space. When the heater heats the cathode it produces electrons (which can be replenished by supplying the cathode with a fresh supply of electrons by electrically connecting it to a negative voltage supply). As the electrons are emitted from the cathode they can be attracted to another cylindrical conductor known as a plate if it is charged to a positive potential. The plate is connected to a positive voltage source which attracts the electrons from the cathode. Between the cathode and plate are one or more “grids” which are screens of wire. The grid can be connected electrically to an outside voltage source. If the grid is at a potential that is more positive than the cathode but less positive than the plate then electrons can be made to flow to the plate. Since electrons are repelled by negative charges if the grid is connected to a potential that is more negative than the cathode then electrons will be repelled and will not reach the plate. Thus a vacuum tube can act as an amplifier since a small signal applied to the grid can control a larger voltage flowing from cathode to plate.

In the late 1950’s and early 1960’s transistors existed and were being used in electronic devices, however they were not as reliable at high frequencies and were more expensive to produce. Vacuum tubes were still less expensive for a time due to the mass production facilities that already existed for their manufacture.

In our picture we show a 2CW4 and a 6CW4. Both are triodes. The first number indicated the filament voltage, one being 2.1 volts and the other 6 volts. The 4 indicated four elements inside the tube, a filament, cathode, grid, and plate. These tubes are triodes and were used as part of the tuner circuit of early color television sets.

To learn more please visit these pages:

A reproduction of an article from “Practical Television” magazine from December 1962. This article has a great diagram showing the construction of Nuvistors as well as example circuits that used them.

An article with some excellent pictures of “Acorn Tubes”… a style of vacuum tube that were the smallest tubes before the production of the Nuvistor. Also some interesting links to some reproductions of 1960’s era electronics magazines relating to amateur radio and “high frequencies”

Wikipedia entry on Nuvistors which includes a useful list of part numbers and types.

(insert standard disclaimer on wikipedia article accuracy and non-primary-ness here)


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