The Nuvistor was the final evolution of the thermionic valve as a general purpose active circuit element. Although valves continue to be used in specialised applications, e.g. CRTs, RF power amplification, by March, 1959 when RCA introduced the Nuvistor, there was already serious competition from the transistor. Above, left, is an example of the first released Nuvistor type, the 7586, manufactured by Philips at Eindhoven and branded 'Mullard' for the U.K. market. The 7586 is a medium mu triode. Here is its data sheet from RCA HB3 data library, 1961. On the right is an example of an RCA 6CW4 high mu triode.

Nuvistors have very low inter electrode capacitances and transit times which means they are usable at VHF and low UHF frequencies, where they considerably out performed the transistors then available. They are the end stage of a miniaturisation process (illustrated below) that had continued from the 1920's in an effort to improve the high frequency performance of RF amplifiers.

size comparison
Left to right: 7586 Nuvistor, EC900 frame grid UHF triode, ECC83 twin triode, 6SN7 twin triode

All Nuvistors share the same twelve pin base (pin 11 never existed AFAIK), a 'Twelvar' - (JEDEC E5-65), although only the needed pins are present on the valves.

Nuvistor Base View
Basing of the 7586 Nuvistor, photo, pin-out, base drawing.

Here is a list of the more frequently seen Nuvistors

An RCA press release March/April 1959 said:

"Although transistors are still a "natural" for many low-level applications, the Nuvistor does provide certain significant advantages: Nuvistors, being in the tube family, are high-impedance devices -- circuit components are generally less expensive.

'ELECTRONIC DESIGN', April 15, 1959, p. 3, said:

"Tube manufacturers have unveiled, in recent weeks, drastically new concepts and techniques aimed to keep them in the race with the transistor industry. Smaller than a thimble, more rugged and efficient than present tube designs, and particularly suited for mechanised production, the "Nuvistor" represents a radical departure in the electronic-tube concept. Developed by the RCA Electron Tube Division, triode and tetrode versions have already been demonstrated in TV tuners reduced to one -third the volume of conventional TV tuners."

© Andy Cowley, 2005    Home