From Batteries (DC) to alternating electric current (AC)

Before Edward S.”Ted” Rogers,Sr., put radio station CFRB on the air in Toronto on February 19,1927, radio stations around the world relied on direct current (d.c.) for their power supplies as provided by batteries and/or motorized generators. The alternating current (a.c.) from power systems could not be used for heating filaments in the audio circuits because it produced an obnoxious hum – hence low-voltage batteries were commonly used. Further, to produce the high-voltage direct current and/or the low filament voltage required by transmitting tubes, electric a.c. motors were coupled mechanically to d.c. generators. This set-up served the purpose but it was expensive and unreliable.

Earlier, another Canadian, Reginald Fessenden had demonstrated in 1900 that radio signals, until then limited to dots-and-dashes, could be “modulated” to carry voice, music and other sounds. Then, in 1902, Fessenden went on to patent another invention of his – the “heterodyne principle” which, as it was perfected, made it easier to tune a radio by using only one instead of as many as four knobs.

In 1925, Edward S. (Ted) Rogers in Toronto scored a break-through in radio receivers. His achievment resulted from his experiments in developing radio tubes employing an “indirectly-heated cathode”. This proved to be a major advancement for radio – particularly so for receivers. Before Rogers’ invention, alternating current could not tbe used to heat the filaments of tubes because of the severe hum caused in the receiver. These early tubes used a filament (as in a lamp) for the “cathode” element (when it was activated, it became hot and emitted electrons). Rogers’ invention shielded the filament with a metal sleeve so that the sleeve was heated by the filament inside it. That sleeve became the cathode” element, and the filament was re-named as a “heater” for the cathode. This development eliminated the hum when the heater was applied with alternating current.

In addition, while rectifier tubes that could convert AC to DC had been invented, they were not used in broadcasting – neither for home receivers nor for transmitters. Ted Rogers applied their principles to develop a rectified AC – power supply to substitute for the high-voltage “B+” batteries in receivers. Thus, all batteries were eliminated. Neither the 6-volt “A” batteries nor the 45-volt “B” batteries were necessary.

After developing this revolutionary receiving tube, Ted Rogers and his brother Elsworth started a new company to make receivers using these tubes and the rectified power supplies. Their father, Albert Rogers, had financed the operations with a holding company incorporated as Standard Radio Manufacturing Corporation Limited. (In 1928, the name was changed to Rogers Majestic Corporation Limited) Standard controlled both Rogers Radio Tube Company and Rogers Batteryless Radio Company – the latter. the manufacturer of the receivers. Models were produced under the names Rogers Majestic and DeForest-Crossley.

In August of 1925, the first Rogers Batteryless Radio Receiver was publicly unveiled at the Canadian National Exhibition in Toronto. For the ensuing two years, these Rogers radio receivers were the only batteryless radios manufactured in North America.

In his book Broadcast Policy Development (1982), Frank Foster recalled that the invention of the batteryless radio by E.S. Rogers had an indirect effect on the development of policy for broadcasting. “His batteryless radio increased the popularity of radio broadcasting. With an increase in the number of radio listeners there was a corresponding increase in the demands for a distinctive Canadian system”.

Ted Rogers went on to adapt his “batteryless” concept to creating the first radio broadcasting transmitter in the world that operated without batteries and generators, solely on AC current supplied by power companies. In 1927, Ted Rogers founded CFRB in Toronto.

See the history of CFRB Toronto.

Compiled by:

Clive Eastwood 
Vice-President, Engineering (ret.1986) 
CFRB Limited

J. Lyman Potts 
Vice-President (ret. 1981) 
Standard Broadcasting Corporation

June, 2003