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Quadruplex videotape
A reel of 2-inch quadruplex videotape compared with a miniDV videocassette
Media typeMagnetic tape
EncodingNTSC, PAL
Developed byAmpex
UsageVideo production
Ampex VR-2000

2-inch quadruplex videotape (also called 2″ quad video tape or quadraplex) was the first practical and commercially successful analog recording video tape format.[1] It was developed and released for the broadcast television industry in 1956 by Ampex, an American company based in Redwood City, California.[2] The first videotape recorder using this format was built the same year. This format revolutionized broadcast television operations and television production, since the only recording medium available to the TV industry until then was Motion picture film.

Since most United States network broadcast delays by the television networks at the time used kinescope film that took time to develop, the networks wanted a more practical, cost-effective, and quicker way to time-shift television programming for later airing in Western time zones than the expensive and time-consuming processing and editing of film. Faced with these challenges, broadcasters sought to adapt magnetic tape recording technology (already used for audio recording) for use with television as well. By 1954 the television industry in the US was consuming more film stock than all Hollywood studios combined.[3]

The term "quadruplex" refers to the use of four magnetic record/play heads mounted on a headwheel spinning transversely (width-wise) across the tape at a rate of 14,386 RPM[4] (for 960 recorded stripes per second) for NTSC 525 lines/30fps-standard quad decks and at 15,000 RPM (for 1,000 stripes per second) for those using the PAL 625 lines/25fps video standard. This method is called quadrature scanning, as opposed to the helical scan transport used by later videotape formats. The tape ran at a speed of either 7.5 or 15 in (190.5 or 381.0 mm) per second; the audio, control, and cue tracks were recorded in a standard linear fashion near the edges of the tape. The cue track was used either as a second audio track, or for recording cue tones or time code for linear video editing.[5]

The quadruplex format employs segmented recording; each transversely recorded video track on a 2-inch quad videotape holds one-sixteenth (NTSC) or one-twentieth (PAL)[6] field of interlaced video. (For NTSC systems, the math suggests 15 transverse head passes, each consisting of 16 lines of video, are required to complete one field.) This meant that 2-inch quad did not support "trick-play" functions, such as still, shuttle, and reverse or variable-speed playback. (In fact, the quadruplex format could only reproduce recognizable pictures when the tape was playing at normal speed.)[7] However, it was capable of producing extremely high-quality images with a horizontal resolution of about 400 lines per picture height, and remained the de facto industry standard for television broadcasting from its inception in 1956 to the mid-1980s, when newer, smaller, and lower-maintenance videotape formats such as Type C videotape superseded it.[8]

There were three different variations of 2-inch quad:

Most quad machines made later in the 1960s and 1970s by Ampex can play back both low and high-band 2-inch quad tape.[9]


Time-shifting of television programming for the Central, Mountain, and Pacific Time Zones by the networks in the 1950s (in order to broadcast their programming at the same local time in each time zone) using kinescope films was quite a rushed and perilous ordeal. This was because there was minimal time for the local TV stations to receive video for the programming from the East Coast (live via leased microwave relay or coaxial cable circuits provided by the phone company (AT&T)), to record it to kinescope films, and to develop the film to be aired. This usually meant the kinescope was aired almost immediately after it came straight out of the developing equipment, still warm from the film dryer. These were referred to by the networks as "hot kines". By 1954, the networks used more raw film stock for kinescopes than all of the Hollywood film studios combined, spending up to $4,000 per half hour.[10][11]

Ampex, seeing the impracticality of the prototype BCE and RCA VTRs, started to develop a more practical videotape format with tape economy in mind, as well as providing a solution to the networks' West Coast delay woes. Starting in 1952, Ampex built the Mark I prototype VTR,[12][13] using 2 in (51 mm)-wide tape. Ampex decided that instead of having the tape move at high speed past a stationary head to record enough bandwidth for video, the head would be made to move rapidly across the relatively slow moving tape. This resulted in the Mark I using arcuate scanning, which consisted of a spinning disk with a face (where the heads were mounted) which contacted the tape (as opposed to the edge of the headwheel with transverse quadrature scanning). This resulted in an arc-shaped track being recorded across the width of the tape.[14] Arcuate scanning resulted in a head-to-tape speed of about 2,500 in/s (63,500 mm/s), but problems with timebase stability of the reproduced video signal from the tape led Ampex to abandon arcuate scanning in favor of the more reliable transverse scanning system.[15][16]

Ampex continued through the mid-1950s with the Mark II[17] and Mark III rototype recorders.[18]

The Mark IV[19] was the machine first publicly demonstrated at the National Association of Radio and Television Broadcasters (now the NAB) convention (the NAB Show) in Chicago on April 14, 1956. After William Lodge of CBS finished his speech, the Mark IV replayed his image and words almost immediately, causing "pandemonium" among the astonished attendees.[10] The earlier Mark III was given some cosmetic improvements, and was also demonstrated at Ampex headquarters in Redwood City the same day. Both demonstrations were a success, and Ampex took $2 million in orders for the machine in four days.[10]

The VR 1000-B model (1961)
The quadruplex system

Ampex later released the first models of quad VTR based on the Mark IV which were also prototypes, the VRX-1000,[20] of which 16 were made. Machines made afterward were the final production models, and were designated as the VR-1000.[21] The advertised price for the Ampex Videotape Recorder in late 1956 was $45,000 (equivalent to $504,000 in 2023).[22]

In 1957, shortly after Ampex's introduction of the 2-inch quad format, RCA introduced a quad-compatible VTR, the TRT-1A. RCA referred to it as a "Television Tape Recorder", since the word "videotape" was a trademark of Ampex at the time.[23]

Ampex developed and released updated and improved models of their quad decks, beginning with the VR-1000B in mid-1959. At that time, Ampex advertised that some 360-plus VR-1000s had been sold worldwide, more than 250 in the U.S.—roughly 30 at each network, 100 by independent stations, and 20 by production companies.[24] The second-generation VR-2000[25] appeared in 1964. followed by a scaled-down economy version, the VR-1200, in 1966 and the AVR series of VTRs, AVR-1, AVR-2, and AVR-3 in the 1970s. The AVR-2 was the most compact of quad VTRs, using conventional 120 volt (V) single-phase household-type AC power to operate, rather than the 208 or 220 V three-phase AC power required by larger quad machines. RCA released later models of quad VTRs as well, such as the TR-22, TR-70, and TR-600.[citation needed]

CBS was the first television network to use 2-inch quad videotape, using it for a West Coast delay of Douglas Edwards and the News on November 30, 1956.[26] The CBS show Arthur Godfrey's Talent Scouts on December 24, 1956, became the first entertainment program to be broadcast live to the nation from New York and taped for a time-delayed rebroadcast in the Pacific Time Zone.[27][28] On January 22, 1957, the NBC game show Truth or Consequences, produced in Hollywood, became the first program to be broadcast in all time zones from a prerecorded videotape.[29]

The engineers at Ampex who worked on the development of 2-inch quadruplex videotape from the Mark I to the VR-1000 were Charles Ginsburg,[26] Alex Maxey, Fred Pfost, Shelby Henderson, Charlie Anderson, and Ray Dolby (who later went on to found Dolby Laboratories).[30][31]

As two inch machines became more reliable, they began to see use in outside broadcast (OB) production. The massive machines required their own truck to house and were incredibly labour-intensive requiring considerable on site maintenance. Despite this, these machines allowed for OB video engineers to provide instant replays and generate opening sequences over which captions could be added.[32]

Product models


Ampex VR2000 Amtec, Colortec and Procamp at DC Video, [1],
Ampex AVR 3

The VR-2000 & VR-1200 (and the VR-1100E & VR-1195, as well as some updated VR-1000 VTRs) used modules to correct the playback time base errors of the videotape.[49]


Bosch Fernseh

Комета (Kometa), Soviet Union

ЛОМО (LOMO), Soviet Union


2-inch quad fate

2-inch quad is no longer used as a mainstream format in TV broadcasting and video production, having long ago been supplanted by easier-to-use, more practical and lower-maintenance analog tape formats like 1" Type C (1976), U-matic and Betacam. Television and video industry changes to digital video tape (DVCAM, DVCPro and Digital Betacam) and high-definition (HDCAM) made analog tape formats increasingly obsolete.[99]

Operation of VR-1000-era machines required the skills of a highly trained video engineer. When a tape was changed, the operator spent as much as half-an-hour, "lining-up" the VTR — that is, carrying out specialized technical adjustments to calibrate the machine to the tape before it was ready for playback. From VR-1200/2000 onward, improvements in head manufacturing/refurbishing tolerances, timebase correction, and greater thermal stability of solid-state electronics made tape changes possible in under a minute and needed servo calibrations only once per shift. From AVR-1 onward, servos were self-calibrating and tape changes as fast as the operator could articulate threading.[100]

The few quadruplex VTRs which remain in service are used for the transfer and/or restoration of archival 2-inch quad videotape material to newer data storage formats, although mainstream TV serials from the 1950s to late 1960s have mostly already been remastered onto more modern media some years ago, even digitized within the last decade.[101]

Bosch Quad VTR Model BCM 40
Ampex AVR-2
Ampex AVR-2 Video Head


The tape used in quadruplex machines may have magnetic particles oriented transversely, to increase the magnetic field strength of the tape when read transversely. This allows for higher signal to noise ratios and the possibility of reducing linear or longitudinal tape speeds. The particles are oriented by applying a strong transverse magnetic field during manufacturing after the particles are applied but before the tape is baked to fix the particles in place.[103][104][105]

See also


General references

Inline citations

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