Back in the good old days of radio manufacturing, roughly 1930 – 1950, many companies were on the lookout for any idea or feature that might distinguish their models from the many sets available to the public. One of the more popular features to emerge was some provision for automatic tuning. Just as programming a video cassette recorder is a mystery for some modern consumers, accurate tuning was a similar chore for many radio listeners of that time. Also, most of the better-quality receivers had features such as high-fidelity audio circuitry and shortwave reception capability, advantages that might be lost or severely diminished should the receiver be mistuned.
Consequently, on many medium- and high-priced radio sets, manufacturers and engineers devised various mechanical or electronic tuning systems designed to free the average listener from the perceived misery of incorrectly-tuned receivers. These automatic tuning systems came in many forms, from elaborate electro-mechanical contraptions (with attendant servicing problems) to simple no-nonsense devices that did little more than spin the tuner to a preset station.
Some of the more prominent automatic tuning systems included (by manufacturer):
RCA : Throughout the middle and late 1930s, many of RCA’s top and medium-line models featured a motor-driven stepper-type system known by the rather ostentatious name of the “Magic Brain”. This was a complicated affair of eight discs and many gears mounted on and around the tuning capacitor shaft, all driven by a reversible electric motor. Metal contacts, preset to each preferred broadcasting station, rode along the rim of each disc, and these contacts were wired to station pushbuttons on the front panel.
When the listener pressed a station button, the motor spun the disc assembly one way or the other until a gap in the disc reached the contact corresponding to the button. At that point, power was cut to the motor, the desired station was (presumably) tuned in, and the automatic frequency control (AFC) circuit cleaned up any remaining error in tuning.
Unlike most systems, the Magic Brain apparatus required a special wrench for setting the stations. This tool was apparently the first thing lost by radio owners, as few of the wrenches have survived to the present.
Midwest : Midwest’s tuner was motor-driven, with the shaft of the motor also serving as the front-panel tuning control. Coupled to the motor, via a cord and pulley system, was a large bakelite disc (mounted on the same shaft as the tuning capacitor) with a metal rim and two air gaps. Metal finger-type connectors were placed along the rim, with each finger corresponding to a preset station. Selector buttons on the receiver’s front panel were wired to each metal finger. When the listener pressed one of the buttons, the motor spun the disc until the air gap was directly underneath the finger corresponding to the button pressed. This broke the circuit supplying power to the motor, leaving the tuning capacitor in the correct position to receive the desired station. As in other systems, AFC completed the tuning process.
This system employed a powerful high-RPM electric motor. Users of these sets must have been a bit surprised, the first few times they used the automatic tuning feature, by the sudden whipping of the dial pointer across the face of the dial.
Philco : Philco’s design for their top-of-the-line models rejected a motor system in favor of a purely mechanical tuner. Their system involved a dial that resembled that of an ordinary telephone, with a rotating handle in place of the traditional finger stop. Small windows around the dial contained printed station tabs, marking the listener’s preferred stations. The listener pulled the handle forward a small amount, rotated it around to the desired station just below the small window, and pushed the handle back in. The mechanism then engaged a preset stop, turned the AFC circuit back on, and the result was a correctly-tuned station.
This system was, within a few model years, abandoned in favor of a simpler design. Later Philco models employed a less-complicated arrangement of pushbuttons wired to adjustable coil/capacitor combinations, preset by the user to the desired stations.
Montgomery Ward, Sears Silvertone, and various smaller manufacturers: These companies used a dial that, like Philco’s system, resembled an old-style telephone dial. Pushbuttons arranged around the circumference of the dial were connected to preset coil/capacitor combinations; pressing the appropriate button brought in the desired station. This system was independent of the main tuning control; a separate pushbutton was required to return to the front-panel variable tuning control. In later years, this system evolved into a modified pushbutton system that manipulated the main tuning control, similar to what was standard on automobile radios. This system had the advantage of being simpler mechanically, easier to service, and required less effort on the listener’s part to set up the desired stations.
Though mechanical pushbutton tuners remained a standard feature of automobile receivers until the advent of the digital era, improvements in radio circuitry gradually diminished the need for automatic tuning systems in home radio receivers. Today, these automatically-tuned radios are a special interest among collectors, particularly those willing to undertake the often difficult restoration work.
Ghirardi, Alfred A., Modern Radio Servicing
. New York
: Radio & Technical Publishing Co., 1935.
Ghirardi, Alfred A., Radio Troubleshooter's Handbook
, 3rd Edition. New York
: Murray Hill Books Incorporated, 1943.
Staff of the P.R. Mallory Company, MYE Techincal Manual
. Indianapolis, Indiana
: P.R. Mallory & Co., 1942.