Nuvistor

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RCA 6DS4 "Nuvistor" triode vacuum tube, ca. 20 mm high and 11 mm in diameter 6DS4NuvistorVacuumTube.jpg
RCA 6DS4 "Nuvistor" triode vacuum tube, ca. 20 mm high and 11 mm in diameter
Nuvistor with U.S. dime for scale Nuvistor 530.jpg
Nuvistor with U.S. dime for scale

The nuvistor is a type of vacuum tube announced by RCA in 1959. Nuvistors were made to compete with the then-new bipolar 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 few tetrodes and pentodes were made; [1] nuvistor tetrodes were taller than triodes.

Contents

Nuvistors are among the highest-performing small-signal radio-frequency receiving tubes, largely due to low stray capacitance and inductance 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 in television sets (beginning with RCA's "New Vista" line of color sets in 1961 with the CTC-11 chassis), radio receivers and transmitters, audio equipment, and oscilloscopes. RCA discontinued their use in television tuners in late 1971.

Nuvistor applications included the Ampex 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 the Neumann U47 studio microphone. [2] Tektronix used nuvistors in several of its high end oscilloscopes of the 1960s, [3] before replacing them later with solid-state JFETs. Nuvistors were used in the Ranger space program and Russian-made ones (with soldered pigtail leads, more reliable than sockets) [1] were used in the Soviet MiG-25 fighter jet, presumably to radiation-harden the fighter's electronics; this was discovered following the defection of Viktor Belenko.

Pin layouts

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:

Types

Nuvistor triode 6S52N. Full (right), without case (left), with flying leads. USSR, 1970s. 6C52H.jpg
Nuvistor triode 6С52Н. Full (right), without case (left), with flying leads. USSR, 1970s.

Dissection of a Nuvistor triode tube

Parts of a small Nuvistor triodePictures
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 tube.jpg
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. 7586 Nuvistor triode tube - bottom view.jpg
The metal envelope has been removed. View of the tube base, anode or plate and support pins. 7586 Nuvistor triode tube - internal top view.jpg
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. 7586 Nuvistor triode tube- internal bottom view.jpg
The anode has been removed. The vertically oriented, mesh wire electrode is the control grid. 7586 Nuvistor triode tube - the grid.jpg
The control grid has been removed. The vertically oriented electrode is the cathode. The indirectly heated cathode surrounds the heater. The electron emitting portion of the cathode is the white-colored oxide coating, typically barium oxide or strontium oxide. 7586 Nuvistor triode tube - the cathode.jpg
The cathode has been removed. The heater is tungsten wire coated with a refractory dielectric material of high thermal conductivity. 7586 Nuvistor triode tube - the heater.jpg

References

  1. 1 2 3 4 5 "Nuvistor Valves". The Valve Museum. n.d. Retrieved 1 February 2025.
  2. ↑ "History of the VF14 tube and the Phaedrus Audio equivalent VF14M". Phaedrus Audio. 2018.
  3. ↑ "Nuvistor". TekWiki. Retrieved 2025-01-14.
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