VACUUM TUBE TERMINOLOGY
■ Cathode — The element from
which electrons are generated.
■ Control grid — A grid designed to
■ Grid — An element that acts to
control electron flow from cathode
■ Element — One of the tube’s electrodes that performs an electrical
■ Octal — A tube with eight pins.
■ Pins — The external connections to
a tube’s elements.
■ Envelope — A tube’s outer shell.
■ Filament or Heater — The element
that heats the cathode.
■ Plate — The element at which
electron flow terminates.
■ Gassy — A tube whose vacuum
has been contaminated by gas.
■ Screen grid — A grid designed
to perform protective or isolation
■ Getter — An electrode that absorbs
gas molecules to preserve the
■ Valve — The English term for a
informed by magazines such as Hugo
Gernsback’s Modern Electrics, several
hundred thousand citizens were
engaged in some form of radio experimentation by the start of World War I.
Licensing of these amateurs or “hams”
began in 1912 and the American
Radio Relay League was formed in
1914. Both the RCofA and ARRL are
still in existence today!
Broadcasting and Riding
Radio captivated the public interest
in the early 1900s much as the Internet
did a century later. Broadcasting got its
start in 1909 as Charles Herrold began
transmitting from his technical school in
San Jose, CA. After the war ended,
interest in receiving broadcasts soared.
KDKA in Pittsburgh, PA received the
first broadcasting license in 1920 and
Herrold’s station became KCBS the
Early broadcasters used new
amplitude modulation (AM) technology, allowing them to provide speech
and music to the listening public. AM
broadcasting was made possible by
the new and powerful vacuum tubes
developed for the military during the
war. These tubes could develop powerful signals of hundreds (!) of watts
on the long-wave bands between 545
and 220 meter wavelengths (1,350
to 550 kHz). By 1923, broadcast
programs were heard every evening
throughout the United States.
Before 1920, most radio engineers
were convinced that the longer the
wavelength of the radio wave (or the
lower its frequency), the greater its
range. Thus, the most important radio
services — military, commercial, and
broadcasting — preferred radio wavelengths of hundreds of meters. In 1923,
the first “frequency bands” were created, relegating amateurs to the “
worthless” bands with meager wavelengths of
200 meters or less (1.5 MHz or higher).
This turned out to be good for the
amateurs or “hams.” They rapidly discovered that the short-waves supported
communication over extremely long
distances. (The secret turned out to be
signal reflections from the ionosphere
and ground.) In November of 1923,
amateurs made the first two-way,
short-wave transmissions across the
Atlantic between 1BCG (a station in
Massachusetts sponsored by the Radio
Club of America) and Leon Deloy,
F8AB in France. Distance records fell
rapidly with the only frequency limits
being those of vacuum tube technology. New tubes and receivers were
vastly more sensitive than before,
allowing communications around the
world with powers of a few watts.
Soon, the services that had clamored for long-wave assignments were
demanding short-wave spectrum from
the new Federal Radio Commission. The
late 1920s were a tumultuous time of
rapidly advancing technology as radio
permeated every aspect of modern
life. Nations found themselves in
competition for spectrum access as
signals routinely ignored
national boundaries. This
grand awakening culminated in the formation
of the International
in 1934 and created
modern radio spectrum
FIGURE 5. The circuit
of a regenerative
through the tickler coil