Description
This article is from the Antique Radios
And Phonographs FAQ, by Hank van Cleef vancleef@netcom with
numerous contributions by others.
53 Dating Old Radios By Their Tube Complement: p1 Older radios
Home entertainment radio began in 1920. KDKA in Pittsburgh generally
has gotten credit for being the first commercial broadcast station. The
two major receiving tubes available at the time with the UX201 and the
UV199, as they were called at the time. The UX201, later revised and
called 01A was a low mu triode. The V99, as the UV199 came to be
termed, was derived from a telephone amplifier triode, developed
during WWI. Several manufacturers built sets, but the most predominant
in the collector market is the Atwater Kent neutrodyne TRF set using
01A's driving headphones. A standard inexpensive set used regenerative
feedback to achieve gain. These were prone to oscillate, squawk, and
whistle, and created no end of radio frequency interference, and rapidly
lost favor, particularly in high-density metropolitan areas.
The first commercially significant superheterodyne receiver was the
RCA "catacombs" receiver of 1924. This set used V99's, a 42 KC IF
frequency, and a headphone-driving-a-horn "loudspeaker." Both the
A-K and the RCA sets required three DC voltage supplies.
The A supply (5 volts DC for 01A, 3.3 volts DC for V99) heated the
filaments. The B supply, typically 90 volts, provided plate voltage.
The C supply, ranging between 9 and 15 volts, and connected as a
negative supply, was used to bias the tube grids. RF gain was
controlled by a rheostat which controlled the filament voltage. These
three voltages were supplied by lead-acid storage batteries, with a
Tungar bulb charger for charging the batteries when the radio was not
being used. All of the RF stages, and the catacombs superhet local
oscillator, were tuned by separate dial knobs.
If this sounds like the definition of a kloodge, it was. I had examples
of both an O1A Atwater Kent and an RCA "portable" (ran on dry batteries)
catacombs set, complete with lead-acid batteries and Tungar charger, at
the end of WWII. These sets sold by the thousands, but were obsolete by
1929, and most of them were discarded when their storage batteries wore
out. Worth noting that "Philco" is a contraction of "Philadelphia
Storage Battery Company." It is also worth noting here that RCA, or
"Radio Corporation of America," was not a separate company until 1929,
but a patent pool and sales company owned by General Electric,
Westinghouse, and AT&T. The phonograph fans will, no doubt, describe
how the Victor Talking Machine Company and Radio Corporation of America
became RCA Victor.
Automatic volume control methods were developed around 1925. AVC, which
is synonymous with the term "Automatic Gain Control" (AGC), allowed sets
to operate at much higher input sensitivity, and to reduce that
sensitivity to prevent overloading in the presence of a strong signal.
Methods of tracking RF stages and a local oscillator operating at some
difference frequency were also developed in the mid-late 1920's. The
final developments needed to build a mains-powered single knob tuning
"modern" superheterodyne radio were filaments capable of working on AC
without developing hum, a suitable high-voltage rectifier, and a tube
with high plate resistance. The first two appeared around 1928 in the
form of the 26 and 71A tubes and the 80 rectifier. While these were not
the actual "first" devices, they appear in almost all of the early
mains-powered radios. The third came about a year later in the form of
the UY224 tetrode, later known as the 24A. The 24 also had another
recent innovation, the indirectly-heated cathode, which allowed the
cathode element of each tube to "float" at a different voltage from the
heater supply DC reference.
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