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1955: Chrysler's All-Transistor Mopar Car Radio

By Rick Hirsh

Chrysler and Philco announced that they had developed and produced the world's first all-transistor car radio in the April 28, 1955, edition of the Wall Street Journal. Chrysler made the all-transistor car radio, Mopar model 914HR, available as an option in Fall 1955 for its new line of 1956 Chrysler and Imperial cars, which hit the showroom floor on October 21, 1955. The all-transistor radio was a $150 option.

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The first all-transistor car radio was a major advance, because it used less than 10% of the battery power of conventional car radios; it also required less maintenance and eliminated the vibrator.

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Chrysler's Mopar model 914HR was also Philco's model C-5690; Philco made this all-transistor car radio for Chrysler. Philco had originally redesigned the Chrysler's Mopar model 912HR, a five push-button "Town and Country" AM radio with an electronic signal-seeking "Electro-touch" tuning bar, that had nine vacuum tubes inside. Philco essentially redesigned the inside circuitry with 11 transistors, and no vacuum tubes.

If the customer also ordered Chrysler's optional Highway Hi-Fi in-car record player, Philco added an extra transistor in its circuitry, for the phono pre-amplifier (2N43) - making a total of 12 transistors inside. The letters "HR" after the model number stand for "High Road" and contains the extra 2N43 transistor.

News of the Philco all-transistor car radio model C-5690 was announced in its 1955 annual report, along with the company's work with Chrysler Corporation.

Author's Notes: Both the Chrysler 1955 Mopar model 902 and 1956 Mopar model 912HR were five push-button "Town and Country" AM radios with an electronic signal-seeking "Electro-touch" tuning bar. Both were vacuum tube radios, that used the same front radio cabinet design as the all-transistor Mopar model 914HR.

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The Mopar Model 914HR all-transistor car radio's circuitry also included the Philco "Surface-Barrier" transistors, the world's first high-speed, high-frequency transistors, developed in 1953; they could be designed for computer usage.

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The rare, highly engineered Mopar model 914HR all-transistor car radio was short lived, and by the end of 1956, Chrysler discontinued it. Chrysler had decided that it would no longer make all-transistor car radios available for its car models during the rest of the 1950s. Instead, Chrysler used "hybrid" car radios, which contained both transistors and vacuum tubes inside.

[Editor's note: The company appears to have barely advertised it, and it is barely visible in the Chrysler and Imperial brochures we have. Nor was it included in the 1955 Annual Report as an upcoming feature.]

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I have also made a YouTube video, which shows the 1955 Philco all-transistor car radio. It contains some 1955 Chrysler dealership promotional film clips on the introduction of some standard and optional equipment. There is also a look at the radio's chassis, which shows all of its transistors and locations.

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General Motor's Delco Radio division was also working on using transistors in its circuitry, for its car radios. General Motors' first use of transistors in its car radios was a "hybrid" car radio that had four transistors and six vacuum tubes, which was used in the 1956 Chevrolet Corvette (Delco model 3725156).

Then, for the 1957 car model year, General Motors used their "first" all-transistor AM car radio, as standard equipment in the $13,074 Cadillac Eldorado Brougham model. This all-transistor 5-push button AM car radio with a signal-seeking tuner (Delco model 7268085), which used 13 transistors in its circuitry and eliminated the vibrator, used less than 10% of the battery power, and also ended the need for warm-up periods.

Like Chrysler, General Motors ended use of its all-transistor radios at the end of its first model year, going back to "hybrid" car radios. The one exception to that was the clever "Trans-Portable" all-transistor AM car radio used in the 1958-59 Oldsmobile, Buick, and Pontiac cars, which could also be removed and used outside the car.

Why the early all-transistor car radios were short lived

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Chrysler's 1955 Mopar Model 914HR all-transistor car radio was quickly discontinued when its 1957 models came out, while Cadillac's 1956 Delco Model 7268085 all-transistor car radio, used on 1957-58 Cadillac Eldorado Broughams, was discontinued with its 1959 models.

Both Chrysler and Cadillac had decided to develop all-transistor car radios to eliminate the number-one problem of vacuum-tube car radios - the vacuum-tube car radio's vibrator. The mechanical vibrating reed contacts inside the vibrator tended to be noisy and tended to fail the most, causing the car radio to stop working.

But the large vacuum tube manufacturers saw that transistor technology was a major threat to their business. In 1956, Tung-Sol helped develop a special 12-volt "space-charge" vacuum tube that could be operated with only 12 volts and eliminated the vibrator. This was a major breakthrough, as the vibrator had been used in vacuum-tube car radios since 1932.

The biggest problem of using these special 12-volt space-charge vacuum tubes in car radios was the fact that they did not supply enough power amplification to the radio's loudspeaker. So in 1956, car radio manufacturers such as Delco, Philco, and Motorola designed a hybrid radio that would use these special 12-volt space-charge vacuum tubes and a single high-power audio output transistor in its circuitry.

Chrysler decided to discontinue all-transistor car radios after 1956. Chrysler then made a decision to start using the new technology of hybrid car radios, by Philco and Motorola, on all of its 1957 cars. The hybrid car radios could be produced at much lower cost than the all-transistor car radios, since transistors, at that time, were still expensive compared to vacuum tubes.

Chrysler used hybrid car radios on all of its models from 1957 to 1963. They started to reintroduce all-transistor car radios again around 1963, when the transistor's sound quality and reliability had greatly improved, and its cost had plunged.

Cadillac also started using hybrid car radios from 1959-63, after introducing them in the 1956-57 Corvettes; and Cadillac also started to reintroduce the use of all-transistors car in 1963.

For more, see Rick's new PDF-format story on Chrysler's hybrid radio, used starting with its 1957 cars.

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General Chrysler-related radio and stereo articles at Allpar:
CD and DVD systems (stereos have a three-letter code on the face plate)
Tape and tape/CD systems
From here to Infinity
CD changers
Classic systems (before tape decks)

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