Shown are some of the many radios that apppeared in this set of exhibits.
Magnavox Co. (Oakland, CA) Amplivox audio amplifier: ca. 1920 This unit amplifies signals from radio receivers or microphones. It uses three type 201 tubes, one for each of three stages of amplification. It has a switch to transfer the signal input between a radio and a microphone, making it useful as a public address system. An interesting message is affixed to the bottom: "This instrument to be used for Audio Frequency Amplification only where messages are not transmitted FOR PAY."
Crystal set: Lemco Equipment Co. (San Francisco), Model 340: 1922
This little unit, built into a small wooden box of the type used to file 3" x 5" cards, is radio at its simplest: The only variable element is the tuning inductor, which has two sets of taps -- one for the antenna to ground tuning circuit, and the second to match the crystal detector and headphone output. However, with a good antenna (and not too many stations within 50 mles), it gave quite satisfactory reception. As no batteries were required for operation, the simple and inexpensive crystal radio was a good choice for the beginning radiophile. The pictured unit was made and labeled for San Francisco's White House Department Store. Crystal radios are still being built today--you can sign up for a MOAH workshop and build your own.
Bodine Electric Co. (Chicago) Basketweave loop antenna: 1922-1925 Early radio receivers required an outdoor antenna of significant length -- 50 to 300 feet -- in order to pick up enough energy for satisfactory reception. This early loop antenna was an effort to cut down on the need for a long antenna, but did not prove particularly successful. External antennas have largely been replaced by the ferrite "loopstick" antenna in consumer radios, which came into wide useage in the 1950s.
Gilfillan Corp (Los Angeles) GN3 Neutrodyne: 1924
Atwater Kent Model 30 TRF: ca. 1926 This six-tube, battery operated receiver originally cost $85.00. There are three tuned RF stages, but they are all tuned simultaneously (gang-tuned) with one knob, a considerable convenience. Audio volume was controlled by varying filament voltage. The radio is housed in a wood cabinet measuring 6.25" high by 20" wide by 6" deep. The top is split, with the front half hinged to allow access to the interior. The batteries are bulky, and reside on a separate shelf, connected to the set via a cable. A second cable connects a speaker. All of the tubes are #201A, except for the speaker amplifier, a #71A.
Magnavox Co. Model T (No. 1217D, TRF) with Eton cabinet: 1926 A five-tube, battery operated radio with three gang-tuned RF stages and a speaker, it covered the AM band from 200 kHz to 1.5 mHz -- almost the same as the standard AM band of today. The tuning inductors are unusual -- wound in a toroidal (doughnut-like) form factor that is relatively difficult to manufacture. Batteries are located on a separate shelf. The receiver used four #201A tubes and a #112A as a speaker driver. The cabinet is also unusual: The working parts of the radio are pulled out, as from a drawer, from the center-front of the cabinet. This would have appealed to the radio hobbyist and the service technician alike.
RCA Radiola Model 17: 1927
Atwater Kent Model 46 TRF: 1928 AC operated with eight tubes, this set has three gang-tuned RF stages. The associated loudspeaker is the Atwater Kent type F-2, an electrodynamic unit with an electromagnet winding that also served as a filter element (choke) for the high voltage DC power supply. This was a standard arrangement before the availability of the high permeability (strong magnetic field) permanent magnets used in more modern speaker designs. It could also be a surprise for the unwary service technician! Tube lineup: 3 #326 RF amplifiers, #27 detector tube, #26 audio amplifier, 2 #71A speaker amplifiers, #80 dual diode rectifier tube for high voltage DC power supply.
Crosley Radio Corp (Cincinnati, OH) Model 168 Gothic cabinet receiver: 1933 This AC operated superheterodyne receiver has seven tubes and is one of the earliest examples of "modern" table-type radio circuit design. Typical of the period, the tubes operated at a filament voltage of 2.5 volts AC, except for the rectifier, which required 5 volts. The husky (and heavy) AC transformer provides these voltages, plus 500 volt AC power (center tapped, so each half of the output winding produces 250 volts) required to generate the 200 volt DC high voltage supply for the tubes. An outside antenna was required. The design featured a single tuned radio-frequency stage, two tubes for the IF frequency oscillator and mixer (It would be another year before the invention of the pentagrid converter, which combined both functions in one tube), and a short-wave band covering 1.7 to 5.5 MHz in addition to the AM band. Except for these three unusual features, the set exemplified the "standard" consumer radio design that persisted into the 1960s and the advent of the AM/FM radio receiver. Throughout this period, cabinet styles and tube changes came and went, but the block diagram of the receiver remained essentially unchanged. Tube lineup: #58 TRF, #58 mixer, #56 IF oscillator, #58 IF amplifier, #2A6 dual section detector and first audio amplifier, #2A5 speaker amplifier, #80 dual diode rectifier.
General Electric Corp Model (Bridgeport, CT) G-50: 1934 With AC operation, wood cabinet and five tubes, this set conforms to the "standard" superhet block diagram. The filament voltage for the tubes has now shifted to 6.3 volts AC (a new standard) for the receiver tubes, but the same heavy multi-winding power transformer is still present. A novel feature is the pushbutton station selector arranged around the tuning dial, recalling the dial of the recently introduced (and, therefor, thoroughly modern) rotary dial telephone. Tube lineup: #6A7 mixer-oscillator, 6D6 IF amplifier, #75 detector and first audio amplifier, #41 amplifier, #80 dual rectifier.
General Electric Corp Model G-50 with plastic cabinet: 1934 This receiver is identical to the original G-50, but has a plastic cabinet, rather than wood. This was something of an experiment, as there were concerns about the fidelity and resonances of sound resulting from the use of plastic, but plastic became the standard cabinet material for less expensive radios as time went on.
Majestic Radio Co. Model 4705: ca. 1945 Operating on battery or AC line power, this seven-tube portable receiver incorporates a tuned RF amplifier for signal selectivity and a low power consumption set of tubes, but is otherwise similar in overall design to other radios of the period. The 1.4 volt filament tubes consume only 60% of the power needed by tubes of the previous decade. Tube lineup: 1T4 RF amplifier, 1R5 pentagrid converter, 1U4 IF amplifier, 1S5 decond detector and first audio amplifier, 3Q4 speaker amplifier (for battery operation), 50B5 speaker amplifier (for AC operation), 35W4 half-wave rectifier for line power operation.
Zenith "Transoceanic" 8G-005YT: 1947
Hallicrafters S-38D AM/Amateur service: 1948 Priced originally at $49.00, this inexpensive AC/DC receiver can be tuned to the AM band and three shortwave bands. It was used by many amateur radio operators as a "starter" receiver. Other than the shortwave feature, this set is just another cookie cut from the standard AC receiver block diagram. Performance is marginal: It has no TRF stage and only one stage of intermediate frequency for minimizing extraneous signals, no calibrated bandspread (fine tuning) for separation of closely spaced signals, and the CW beat frequency oscillator (BFO) has no control for optimum tone adjustment. But it was inexpensive.
RCA Victor Model 68R3: ca. 1955 An eight tube superheterodyne, this receiver was a marginal performer despite the high tube count. There is no TRF stage and only one stage of intermediate frequency (IF) amplification. A single pentode audio output stage provides sound with noticeable distortion. It has internal loop antennas for AM and FM bands, but no loopstick antenna for high- efficiency pickup. Tube lineup: 6BE6 AM pentagrid converter, 6BE6 FM pentagrid converter, 6AU6 local oscillator, 6BA6 IF amplifier, 6SQ7 AM detector, AVC and AM/FM audio amplifier, 6AL5 FM ratio detector, 6K6 power pentode speaker driver and 5Y3 dual diode high voltage rectifier.
Grundig Werks AM/FM Stereo with record player Model SO 101/60PX: ca. 1960 This German-made superheterodyne receiver had eight German tubes and a selenium rectifier for its internal DC power supply. The record player operated at 16, 33-1/3, 45 and 78 RPM. It was originally priced at $240.00. The combined AM/FM design lacks the necessary circuits for good FM performance. This lack was not necessarily obvious near the big cities in 1960, where there were few, but powerful, FM stations. Out in the countryside, its shortcomings were painfully obvious. The audio section of the set was near state-of-the-art, and normally delivered good fidelity with low distortion, significantly better than the average broadcast receiver of the day and an advantage when playing records. Tube linup: ECC85 dual triode RF amplifier, ECH81 pentagrid converter and triode in one tube envelope, EBF89 duodiode (second detector) and pentode (IF amplifier), ECC83 dual audio triode for tone controls, ECC83 dual audio triode for first audio stereo amplifier, two EL95 beam power tetrodes for speaker amplifiers, EM84 "tuning eye" indicator.
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