Vacuum Tube Radio

By the late 1920s, vacuum tube radio equipment replaced the primitive spark-gap systems on most merchant ships. This new equipment could send and receive signals virtually worldwide, by using high frequency or "short-wave" bands. Tube technology allowed radio signals to be tuned with much greater precision than spark-gap.

Although tube equipment could be used for voice transmission, Morse code was more reliable for long-distance signals and continued to be the standard for marine communications. The basic design for tube radio was perfected by the 1930s and continued in use on merchant vessels into the 1980s.

Dr. Lee deForest invented the vacuum tube in 1906. His tube, which he called the "audion," was first developed as a detector of radio waves and was quickly adopted by shipboard operators. Later experimentation, by deForest and others, showed the ability of the vacuum tube to generate radio signals with far greater precision than earlier systems. By 1914 the essentials of tube-based transmitters had been worked out.

World War I led to rapid development of the new technology for military purposes, and during the post-war decade tube-based systems began to replace the spark system as the marine radio standard.

The troopship General John Pope was built in New Jersey in 1943, the first of the "General" class of World War II P2 troop carriers. Her radio equipment is in the case to your left. The Pope served as a naval transport in the Pacific Theater during WW II. She was reactivated as a Military Sea Transport Service vessel during both the Korean and the Vietnam Wars. The Pope was laid-up at Suisun Bay in the early 1970s. Photo SFMNHP, P77-026A353n .

tube followed the work of earlier experimenters. Thomas Edison developed the light bulb with its single filament in the 1880s, and Ambrose Fleming added a metal plate to the bulb around 1900 to produce a detector of radio waves. DeForest added a third element, a wire "grid" which resulted in a vastly improved detector and ultimately the ability to both amplify and generate electromagnetic energy. Ad from Radio News, December, 1929.
in receivers well before tube transmitters were introduced. Purchased privately, sets like this deForest RJ-6 were used without company permission by Marconi and RCA shipboard operators during the spark era. They were much better than the equipment which the company provided. The receivers had to be hidden away when the ship was in port so the company inspectors would not see them.
The Iong-range potential of short-wave radio was not discovered until the 1920s. These high-frequency signals ("short-wave" equals high-frequency) could bounce along between the ionosphere and the ground to achieve virtually worldwide range. Neither the low and medium-frequency signals nor the very-high-frequency bands had this property. Initially allocated for amateur use, the high frequency range was considered to be of little practical use, but ultimately became the principal means of long-distance communication.
1940 THE RCA "4-U" RADIO,
named for its four units of receivers and transmitters, was one of the standard console radio systems aboard merchant ships during World War II. Console sets were produced by the Radiomarine division of RCA and by the Mackay Radio division of IT&T. Using the vacuum tube technology of the late 1930s, the 4-Us were large and heavy, but were suitable for mass-production under wartime conditions and proved reliable through adverse weather and enemy action. Ad from The Nautical Gazette, April 1946.
available for inshore vessels in the late-1930s, became common after World War II. Operating on the 2 to 3 MC band, these compact short-wave units had a range of about one hundred miles. The sets were used on fishing boats, tugs and yachts. In the early 1950s, ocean steamers were equipped with larger radiotelephone sets made by Mackay or Radiomarine. In this 1946 ad, "Johnnie" the bellhop extols the Hudson American set fitted on his cabin cruiser. Ad from Pacific Motorboat, June 1947.
was a smaller and more refined version of the time-tested tube technology of the wartime models. Aficionados consider these sets the pinnacle of a "Golden Age" of radio that pointed the way toward today's compact radio systems. This radio was aboard the Chevron tanker Alaska Standard, and used until 1985. Photo SFMNHP, Demeo collection.
offered the first long-distance voice communication, and was developed during the vacuum tube era. It only became widespread in marine use when transistors replaced tubes, allowing the units to be much smaller and more rugged. The early single-side band radio units, like this set installed aboard the liner S.S. United States, were both large and expensive.
in the radio room of the S.S. Santa Maria. He served for some years as the West Coast head of the Radio Officers' Union. The Santa Maria, built in 1963, sailed for the Delta Line on a South American run and was among the last American passenger vessels. Her radio room represents the last generation of marine radio-telegraphy gear. Photo SFMNHP, Chow collection.