Physical Description: The Radiotron is a tall glass tube that stands 41cm high. The total width of the Radiotron is 25cm. The main glass sphere has a diameter of 18.34 cm. Attached to one side of this sphere is a tubular piece that has an outside diameter of 3.175 cm and an inside diameter of 2.5cm. The tubular piece is extruded 6 cm out from the sphere. The main body has two steel pegs that are used as electrical contact points. At the bottom of the structure there is a steel collar where wires are fed into the Radiotron. The Radiotron has many important internal parts; comprised of steel, steel mesh, and aluminum as seen in the figure which shows a detailed drawing of the Radiotron.

Functional Description: The Radiotron is a triode vacuum-tube, working through a process known as thermionic emission, in which a cathode tube is heated so that it throws off electrons in the surrounding space. Surrounding the cathode is a metal plate which, if positively charged, will attract the ejected electrons, establishing a current. The radiotron is a triode vacuum tube, in which a small metal metsh is placed between the cathode and the anode plate. This mesh, if connected to a negative voltage, can reduce or shut off the stream of electrons from the cathode to the anode. This setup allows for small changes in voltage through the mesh to correspond to large voltage changes in the anode acting as an electric amplifier. The Radiotron is then attached as part of a larger circuit, in the case of our object, likely as a power amplifier aboard a navy ship.


Emily Oppliger, Grayson Hooper, Anthony Miller, Colton Kettlehut, Cam Dulong


Related to vacuum tubes


Physical Object



Physical Dimensions

Height: 41 cm
Width: 25 cm
Bulb Diameter: 18.34 cm
Length: 24.34 cm


Glass, conducting metal and wires, plastic


RCA Corporation


Metal Base of Radiotron: JAN CRC-861 / VT-19 / Made in U.S.A. VI / RCA / H1201
Wooden Base: "High power radioton, circa 1940 (power output stage for a transmitter) Manufactured by RCA for U.S. Navy."
Typewritten Note: "Max plate dissipation 400 watts fil 11 volts at 10 amp. Max plate voltage 3500. Max screen voltage 750. Max screen dissipation 35 watts. Class C amp. Plate voltage 3500, Screen voltage 500, Grid voltage 250, Plate current 300 Ma. Screen current 40 Ma. Grid current 40 Ma. Driving Power 30 Watts. Output 700 watts."

History of the Object

The JAN-CRC-861 Radiotron was built in the United States by the RCA company for the use of the US Navy around the 1940s. The 861 series was widely used within the TBM and TBK series of transmitters within th Power Output stage. RCA was founded in 1919 by General Electric and manufactured high powered radio technology. RCA now produces products like 4K televisions, tablets, smartphones, and other home appliances. It is unclear when and why Michigan Tech acquired this device.

Vacuum tubes were first invented in 1904 by British scientist John Ambrose Fleming while investigating the "Edison effect", now know as thermionic emission and helping design Marconi's trans-Atlantic transmitter (Fleming is the attriuted creator of the "right-hand rule" for relating the direction of magnetic field, conductor motion, and induced electromagnetic force). Fleming was primarily interested in producing a "rectifier" that was an improvement on current "cat-and-whisker" techniques - which were especially vulnerable to vibrations (a problem for naval use).

The tube Fleming produced was a "diode", having only the cathode and the anode. The introduction of the middling mesh was a product of Lee De Forest in 1907, creating the "triode" ("tetrode" and higher versions also exist). De Fores was, like Fleming, interested in producing a better dector (rectifier) for radiotelephonic uses however analysis of contemporary writings indicate he didn't quite understand how his invention worked, especially in it's possible uses as an amplifier/oscillator - even cautioning against having "too much of a vacuum".

Nonetheless, the invention of the triode tube made transcontinental telephony possible for the first time. Vacuum tubes quickly branched out of radiotelephony as uses were found in power grids, tv, and even computers. However with the discovery of semiconductors in the 1940s and transistors in 1960s, Vacuum tubes were gradually phased out in efforts to reduce size, speed and cost and improve reliability. Cathode-ray tubes continued to be used in tvs until recently and vacuum tubes are still used in a variety of locations - Magnetron in microwaves and some high-frequency amplifiers.


MEEM building Room 607


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Emily Oppliger, Grayson Hooper, Anthony Miller, Colton Kettlehut, Cam Dulong, “Radiotron,” Michigan Tech Inventory of Historic Scientific Instruments, accessed May 7, 2021,