The Early History of Videotape Recording

Speaker: Fred Pfost

Fred Pfost spent ten years at The Ampex Corporation in Redwood City directly after graduating from U C Berkeley in January of 1952. He was instrumental in the development of many of the audio, instrumentation and video products that Ampex produced during his stay: a 21-channel instrumentation recorder, a 7-channel FM recorder, a semiprofessional portable audio recorder (model 600), a portable amplifier-speaker unit (model 620), an oil well logging recorder, the V R 1000 videotape recorder and glass bonded ferrite heads for video recording.

Following his employment at Ampex Mr. Pfost did consulting for the next 30 years doing work for 25 different local, national and international companies. He started three companies during that period and developed some breakthrough technologies that set the standards of achievement for various industries.

Several of Pfost’s accomplishments were:

• The computer industries first hard disc data recorder – developed for Data Disc in Mtn. View in 1963 (This technology was licensed to IBM and eventuality became known as the “Winchester Disc”.)

• Stop action-instant replay hard disc video recorder developed for Mactronics in Mtn. View in 1965 (Ampex came out with their version of this device a year later.)

• Video Cartridge Recorder developed for Cartrivision in 1970

• High speed, high tension tape cartridge developed for Newell Research in 1975

• Automatic Robotic Work Station (Automatic Microprocessor Controled Pipetter) for Infinitek (purchased by Beckman Industries) in 1985

• Automatic, spring-loaded, lever-cocked pool cue developed for Automatic Ball Driver, Inc. in 1992

Mr. Pfost has 50 U.S. patents and hundreds of foreign patents.

He was awarded three EMMYs over the years.

1) The Videotape Recorder at Ampex in 1957

2) The Stop-action instant replay recorder at Mactronics in 1966

3) “Lifetime Achievement” on September 29, 2005

This last one was the first time that the Television Academy had ever given a “Lifetime Achievement” award in the technical EMMY category.

When one compares the information content requirements for video recording versus audio recording the ratio is about 1000 to 1. Pulling tape at high speeds is not practical when one considers tape speeds of 10 to 100 feet per second. RCA first tried 360 inches per second (30 feet per second) with 2-track recording and later lowered that to 240 inches per second (20 feet per second). Crosby Enterprises ran at 100 ips (8.3 fps) using a 10-track multiplexed signal. England (BBC) developed VERA that ran at 840 ips (70 fps) for 15 minutes of recording on a 21-inch diameter reel.

Ampex used a rotating head approach with frequency modulation and ran the tape at 15 ips but the head-to tape velocity was 1500 ips (when spinning the head drum at 14,400 revolutions per second). This gave a bandwidth of about 4 MHz, which the industry wanted and needed. This also allowed 1 hour of recording time on a 10.5-inch reel of 2-inch wide tape.

All of these developments were done in thee early 1950s. We, at Ampex, originally used amplitude modulation but later changed to frequency modulation (FM). The original FM circuitry modulated a high RF carrier frequency with subsequent heterodyning down to a frequency that was compatible with recording on tape. This circuitry was followed by a simpler system which directly modulated a multivibrator circuit (with the video signal) that was running at a carrier frequency that could be recorded on the tape system (5 MHz).

The original rotary head orientation wrote arcuate tracks across the 2-inch wide tape. In playback we saw a scalloped output as the heads would cross the tape. It took us quite a while to deduce the cause of this scalloping. We finally decided that the tape was longitudinally orientated and that there was some longitudinal motion of the heads near the start and finish of the arcuate sweeps and only transverse motion near the middle of the arcuate sweeps. Thus the head output would be higher near the tape edges than it would be near the middle of the tape. This would require a large amount of automatic gain control. While I was developing this AGC circuit we decided to just change the head drum orientation to produce only transverse tracks across the entire tape width thus eliminating the variations in output as the head traveled across the tape. We also changed to unoriented tape. I was then put in charge of the video transducer design and the video head assembly design.

This was the configuration used by the whole industry until the advent of the helical scan configuration some 20 years later.

Fifteen thousand “Quad” machines were produced by Ampex over the next 20 years with little change in the mechanical design. This required about 50,000 head assemblies to cover the in-use and replacement schedule. Head life was about 100 hours at the beginning an advanced to around 10,000 hours later with the development of ferrite heads with glass gaps and air bearings.

Space is limited and only preregistered guests will be admitted. There will be no late registration at the event. There will be a cash bar in the meeting room. Please meet your colleagues there rather than in the restaurant bar.

6:00 Check in -- Bar
6:30 Dinner
7:00 Program