John T. Mullin


John T. Mullin
San Francisco, CA, USA
Associated organizations
Ampex Corporation
Fields of study
Radar, Magnetic tape


John T. Mullin reshaped radio and television broadcasting in the 1940s by introducing magnetic tape technology to the industries and developing the first commercial audiotape recorders for the Ampex Corporation.

Mullin was born in San Francisco in 1913 and graduated from Santa Clara University with a degree in electrical engineering. In 1941, he entered the U.S. Army as a private, and rose to the rank of major in the Signal Corps. From 1943 to 1944, he was stationed in England at a Royal Air Force facility where he was charged with improving Allied radar systems. When the BBC went off the air at night, he listened to the only classical musical broadcast available, which was sent from inside German lines. The clarity of the broadcasts was outstanding. They did not pop and click like American broadcasts, which depended on acetate records for playing performances that were not live.

Mullin was convinced that the Germans had developed a superior recording technology, and in the summer of 1944, he set up a lab in liberated Paris to study captured German electronics equipment. He continued to investigate this technology through war’s end, when he went on a fact-finding mission across Germany, which included a stop at underground recording and broadcast studios in Hitler’s bunker. The most important stop was near Frankfurt, where a British officer told him about a high-fidelty German AEG Magnetophon audiotape recorder that could reproduce music with little distortion and a frequency response nearly matching human hearing. When Mullin found some of these magnetophons, he determined that AC bias in the record circuit accounted for their unmatched quality. He applied this insight to the lesser-quality magnetophons he had previously gotten his hands upon, modifying them by adding AC bias.

When Mullin returned to San Francisco in January 1946, he brought along two AEG Magnetophon K-4 decks with spare heads and fifty reels of blank tape. He formed a partnership with William A. Palmer to build a prototype hi-fi tape machine that could record a half-hour radio show. His improved redesign of the magnetophon impressed members of the Institute of Radio Engineers (now the IEEE) with its fidelity to a live performance. The technology had the added advantage of producing editable tracks; before, the masters from which records were produced were pressed into acetate, making editing nearly impossible.

Bing Crosby, who had grown weary of recording live performances of his radio show twice a night for a bi-coastal audience, invested in Mullin’s technology and used it to record his show. Tape-delayed broadcasts would soon become standard practice in the radio industry. Around the same time, Mullin and Parker worked with Ampex Corporation to make the first commercial audiotape recorder, the Model 200

Mullin soon applied magnetic-tape technology to the exploding television market. In 1951, Mullin and Wayne R. Johnson, in collaboration with Bing Crosby Enterprises, developed a prototype video recorder they called the “filmless camera.”

Mullin joined the 3M Company in the 1950s after it bought out Bing Crosby’s electronics company. He worked there until his retirement in 1975.

Further reading

Bing Crosby and the Recording Revolution - A first hand account authored by Robert R. Phillips about Bing Crosby's contributions to magnetic recording

My Ten Years at Ampex and the Development of the Video Recorder - A first hand account by Fred Pfost about his experiences at Ampex