RADIO TUBES

Year Published: 1920s

Creator: RCA

Description: “Radio Tubes” is a somewhat fragmentary, late 1920’s silent educational film providing explanation on functions of the radio tube. The film captures a point in early radio history when rapid innovations were taking place. It includes footage of a Fleming type tube, early portable radios including the RCA Radiola 26 Portable Super-Heterodyne, oscillators and large radio telephone transmitters. In the 1920’s radio tubes, also known as ‘vacuum tubes’, were replacing crystal sets. The film also explores crystal detectors using a galena crystal, how oscillators produce radio frequency currents as well as the transmission of images using wireless telegraphy systems. It also shows the sending of photographs by wire, aka wirephoto, telephotography, or radiophoto. This process, which became prominent in the 1920s, allowed news agencies to transmit images over telephone, telegraph, or radio lines, significantly speeding up the delivery of visual news to newspapers across the country. 0:00 Film opens with a Fleming valve type radio tube (:22). These were considered to be the first thermionic vacuum tube invented by John Fleming in 1904. The tube acted as a detector for radio waves as it converted alternating currents of radio signals into a direct current. A series of title cards and diagrams begin to explain processes occurring within the tube. The filament is heated by electricity created by a battery (:33). Type “A” batteries powered the filaments, while “B” batteries enabled a stronger voltage for the plates. The location of the filament (:36), battery (:42) and vacuum are highlighted (:46). Electrons are thrown from the heated filament (:56). A plate surrounds the filament (1:04) connected to it’s battery (1:12). The plate holds a positive charge (1:17). Negatively charged electrons move towards the positively charged plate (1:32). Footage shows the current flowing in one direction due to the arrangement (1:37). A grid is set between the filament and plate (1:54). A diagram shows the new arrangement (2:10) noting location of the grid (2:15) and grid batteries (2:19). Weak currents produce a negative grid (2:23). Strong plate currents enable a positive grid (2:30). Currents are amplified through properly connected tubes (3:08). Credits acknowledge Western Electric Co. of NYC and RCA (3:22). Western operated from 1869 to 1996 as a subsidiary of AT&T. They were the primary manufacturer, supplier and purchasing agent for Bell System’s telephone equipment. RCA is a company with significant history founded in 1919 in an effort to monopolize the emerging radio industry. Examples feature a situation where the waves of a broadcast station are cut off (3:26) and where the radio frequency is induced in an aerial circuit (3:46). Another example shows the crystal detector (4:09) using a galena crystal (4:15). Crystal sets were popular and cheap for consumers. They would become obsolete by the mid-1920’s replaced by the vacuum tube and it’s powerful amplification abilities. The current flows in one direction through the crystal (4:26). Currents pulsating through “phones” (5:05) produce sound waves (5:10). A man and woman tune their RCA Radiola 26 Portable Super-Heterodyne radio (5:30). This was considered to be the first truly portable radio and weighed 25 lbs. Footage shows the radio tubes within (5:48). The oscillator produces radio frequency currents beginning with the power source connected to the oscillator (5:57). Oscillators enabled the selection of desired stations and were used as transmitters to create a carrier wave for broadcasting purposes. Amplification of oscillator output (6:47) and the effect of the addition of an Audion (8:05). Radio equipment used to transmit photographs (8:23). A negative is set over a glass cylinder (8:28). A broadcasting station featuring a large generator (8:44), amplifiers (8:49) and an oscillator (9:07). Large transmitting tubes are water cooled (9:19)

Online Copy: https://www.youtube.com/watch?v=lEPmm8m5UlA

Metadata Source:YouTube