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Thenuvistor is a type ofvacuum tube announced byRCA in 1959. Nuvistors were made to compete with the then-newbipolar junction transistors, and were much smaller than conventional tubes of the day, almost approaching the compactness of early discrete transistor casings. Due to their small size, there was no space to include a vacuum fitting to evacuate the tube; instead, nuvistors were assembled and processed in a vacuum chamber by simple robotic devices. The tube envelope is made of metal, with a ceramic base.Triodes and a fewtetrodes andpentodes were made;[1] nuvistor tetrodes were taller than triodes.
Nuvistors are among the highest-performing small-signal radio-frequency receiving tubes, largely due to lowstray capacitance andinductance due to their small size.[1] They have excellent VHF and UHF performance, and low noise figures, and were widely used throughout the 1960s for low-power applications intelevision sets (beginning with RCA's "New Vista" line of color sets in 1961 with the CTC-11 chassis), radio receivers and transmitters, audio equipment, andoscilloscopes. RCA discontinued their use in television tuners in late 1971.
Nuvistor applications included theAmpex MR-70, a studio tape recorder whose entire electronics section was based on nuvistors, and studio-grade microphones from that era, such as the AKG/Norelco C12a, which employed the 7586. It was also later found that, with minor circuit modification, the nuvistor made a sufficient replacement for the obsolete Telefunken VF14M tube, used in theNeumann U47 studiomicrophone.[2] Tektronix used nuvistors in several of its high end oscilloscopes of the 1960s,[3] before replacing them later with solid-stateJFETs. Nuvistors were used in theRanger space program and Russian-made ones (with soldered pigtail leads, more reliable than sockets)[1] were used in the SovietMiG-25 fighter jet, presumably toradiation-harden the fighter's electronics; this was discovered following thedefection of Viktor Belenko.
Nuvistor sockets have a standardized layout based on four imaginary concentric circles with the pins laid out at 60 degree angles from the center point of the base. The metal shell has two fins that extend below the base; the larger of these two fins is the key position. Sockets can accommodate up to 12 pins, but usually only five or six are used.
Pins 1, 2 and 3 are assigned to the outermost circle, with Pin 1 located 60 degrees clockwise of the key fin. Pin 2, which is in line with the small fin, is 120 degrees clockwise of Pin 1. Pin 3 is 120 degrees clockwise of pin 2. For triodes, these pins (usually just Pin 2) are the plate/anode connection. For tetrodes, one of these pins is the screen grid connection and the plate/anode has a top cap connection.
Pins 4, 5 and 6 are assigned to the next circle. Pin 4 is in line with the key fin. Pin 5 is 120 degrees clockwise of Pin 4 and the key fin. Pin 6 is 120 degrees clockwise of Pin 5. The pins in this circle (usually pin 4) connect to the control grid.
Pins 7, 8 and 9 are assigned to the next circle. They are in the same lines as Pins 1, 2 and 3 and also increase in order going clockwise. These pins (usually pin 8) connect to the cathode.
Pins 10, 11 and 12 are assigned to the innermost circle. They are in the same lines as Pins 4, 5 and 6 and also increase in order going clockwise. These pins (usually Pins 10 and 12) connect to the heater.
Base 12AQ -- which is used by most triodes, including 6CW4 and 6DS4 -- is the most common connection layout. The connections are:
Base 12AS is the tetrode layout. The connections are:
| Parts of a small Nuvistor triode | Pictures |
|---|---|
| 7586 Nuvistor triode. Two lugs (one large and one small) adjacent to pins 2 and 4 locate the valve in its socket, which is shown alongside. |  |
| 7586 Nuvistor triode. Twelve pins protrude through the ceramic base, some of which are long and form the connections to the heater, cathode, grid and anode electrodes. These short pins support the internal structure, along with the long ones. |  |
| The metal envelope has been removed. View of the tube base,anode or plate and support pins. |  |
| View of the tube base,anode or plate and support pins. Note that there are no mica spacers used to support and separate internal structures, as in normal valves. |  |
| Theanode has been removed. The vertically oriented, mesh wire electrode is thecontrol grid. |  |
| Thecontrol grid has been removed. The vertically oriented electrode is thecathode. The indirectly heated cathode surrounds the heater. The electron emitting portion of the cathode is the white-coloredoxide coating, typically barium oxide or strontium oxide. |  |
| The cathode has been removed. The heater istungstenwire coated with a refractory dielectric material of high thermal conductivity. |  |
