It’s Transistorized!

James Kraus

Regency TR-1 portable transistor radio, November 1954.

The Transistor has been called the most important invention of the 20th century and the key to the dawn of the information age.

The very first consumer product to reap the advantages of solid-state electronics was the Regency TR-1 portable transistor radio, which debuted just in time for the 1954 Christmas shopping season. Due to the small package size and low power consumption of its germanium transistors, the Regency was much smaller than existing tube-powered portable radios with a battery life four to five times greater.

Fairchild Semiconductor TO-18 PNP discrete transistor.

The transistor and its semiconductor companions, the diode and integrated circuit were specifically designed to replace vacuum tubes. They were widely embraced as they were far more rugged, consumed less power, required no warm-up time and occupied only a fraction of the space. They would go on to transform motor vehicles as well as audio equipment, portable televisions and computers.

In the 1950s the only vacuum tubes in automobiles (other than GM cars with Autronic-Eye automatic headlight control or Mirror-Matic auto-dimming rearview mirror-equipped Chrysler products) were found in radios, and this became the entry point for the new solid-state technology.

In addition to the advantages listed above, transistorized radio circuitry would eliminate the mechanical and electrical hum generated by failure-prone vibrator power supplies, which were necessary in automotive applications to convert 6 or 12 volts DC to the 100-plus volts of alternating current needed to power conventional vacuum tubes.

1956 Corvette.

First out of the gate were General Motors and Chrysler. In 1956 GM offered a Delco four-transistor/one rectifier tube hybrid design AM pushbutton Wonderbar signal-seeking radio on the Corvette that offered many transistor advantages without the cost of full transistorization. In the 1950s; transistors, semiconductor diodes and the requisite passive circuit components were still more costly than vacuum tubes. The hybrid radio was the most expensive option on the ‘56 Corvette with the exception of the auxiliary hardtop.

That same year Chryslers and Imperials offered an optional all-transistor radio, but it was too costly and the majority of buyers stuck with the standard tube radio.

’57 De Soto Adventurer.

For 1957 General Motors introduced an all-transistor Delco radio exclusively for their new cost-no-object Cadillac Eldorado Brougham.

Meanwhile, Chrysler switched to their own less-expensive hybrid approach using multiple tubes with a single Philco or Motorola audio output power transistor. GM made their hybrid available on Chevrolets and Pontiacs in addition to the Corvette, and the Ford Motor Company offered a hybrid radio on Ford-branded cars, rolling out transistor technology carefully as to avoid potential reliability issues on their upmarket Mercury and Lincoln divisions.

By 1963 most manufacturers, including Philco (Ford), Delco (GM), Bendix (Chrysler) and Becker (Mercedes-Benz) rolled out all-transistor radios. By the mid-sixties, nearly all car radios were tubeless and fully-transistorized. 

Delco AM Pushbutton All-Transistor radio in 1965 Oldsmobile Jetstar I.

The most adventuresome experiment in automotive transistorization was Chrysler Corporation’s Bendix-developed Electrojector fuel injection system offered on the 1958 Chrysler 300D, Desoto Adventurer and Dodge Custom Royal Lancer D-500. This was a timed port-injection system that triggered injection through timing pulses generated by a signal from the distributor.

The dual throttle bodies of the Electrojector system can be
seen here under a pair of metallic gold air filter housings.
In the foreground is the fuel rail and the four
four injectors of the right bank of a DeSoto 5.9 litre V8.
Don Verity photo.

The Electrojector system took into account ambient temperature, engine temperature and altitude. Alas, electronics were still in their infancy. Transistors, having just been made available in quantity in 1952, were still very expensive, and to in an effort to rein in costs, Bendix used low quality paper capacitors that were prone to failure. In addition, the systems electrical connections were insufficiently sealed against moisture.

The rather haphazardly assembled circuit board
inside the Electrojector control unit. Don Verity photo.

Customer complaints piled in and Electrojection was phased out less than a year after introduction, with little more than 50 cars built with the system. To placate unhappy owners, Chrysler arranged to replace the fuel injection with twin four-throat carburettors at no charge.

1960 Valiant with compact finned-aluminium AC alternator.

Undaunted by their problems with the Electrojector system, Chrysler jettisoned the traditional DC generator; the standard for automotive electrical power generation since 1912, in favour of an AC alternator on their all-new 1960 Valiant. Three positive and three negative semiconductor diodes were utilized for converting the alternating current output of the alternator to direct current.

AC alternators, with their greater efficiency, high idle-speed output and reduced weight and bulk spread quickly throughout the industry.

1960 Chrysler 300 AstraDome instrument pod
with Panelescent lighting, co-developed by
Chrysler Corporation and Sylvania Electric
Products. JC Automotive photo.

Simultaneously, a single germanium PNP switching transistor was used in the 200-volt, 250hz power supply for the advanced glare-free electroluminescent instrument panel display in 1960 Chryslers and Imperials.

Following Chrysler’s brief experiment with electronic fuel injection, the second powertrain implementation of transistorization was the ignition system. By the dawn of the 1960s, higher engine speeds were probing the limits of convention systems as the ignition coils in multi-cylinder, high-speed engines struggled to fully saturate due to limited dwell time, causing reduced current output and a weak spark at the plugs.

Ford 7-litre 427 V8 valve cover badge
denoting optional electronic ignition.

Using a transistor to direct high voltage to the spark plugs allowed higher voltage for a hotter spark without worry about point erosion. With electronic ignition, consistent voltage delivered to the spark plugs can be maintained from idle to 7000+ rpm, while the voltage from a conventional point-fired system might drop 30% or more.

1963 Ford Galaxie 427 with optional electronic ignition.
Amplifier module box can be seen mounted on inner fender.

Ford began offering an optional electronic ignition system on Thunderbirds and 427 V8 Galaxies in the spring of 1963 with a transistor to handle load switching, using very low current through the ignition points; all but eliminating point wear and attendant timing drift. With points performing solely a timing operation at very low current, ignition system maintenance became nearly non-existent to the extent that Ford ultimately marketed the option as the Ford Perma-Tuned Transistorized Ignition System.

GMs Delco-Remy Delcotronic transistor-controlled magnetic pulse ignition system was more advanced, using a contactless magnetic hall-effect unit in the distributor, eliminating ignition points entirely. Without mechanical points, higher engine speeds could be obtained without the possibility of point-bounce.

Delcotron ignition amplifier in 1966 Corvette Sting Ray
mounted in front of and to the left of the radiator.

This was a dual transistor system with a triggering transistor as well as a high-capacity switching transistor. It debuted as optional equipment on 1964 Chevrolets and Pontiacs.

Inside the Porsche 911 Bosch transistorized
voltage regulator, 1965.

Meanwhile, in 1965 Porsche’s new 911 incorporated a Bosch solid-state electronic voltage regulator with a transistor replacing traditional mechanical point contacts.

1967 Fiat Dino with large finned cast-aluminimum amplifier
housing for its Magneti Marelli electronic ignition.

Transistorized ignition became more widespread with the ‘67 Fiat Dino V6 Spider featuring Magneti Marelli Dinoplex ignition as standard equipment in 1967.

Inside the Porsche 911 Bosch CDI ignition amplifier, 1969.

Porsche would follow suit two years later, adding a Bosch electronic ignition system as standard fitment on 1969 Porsche 911 E and S models.

Finally, in 1968 Bosch released what would be the killer app for 1960s solid-state automotive electronics: their new Jetronic electronic fuel injection.

In 1965, Robert Bosch licensed the patents for the ill-fated Bendix Electrojector system. The burgeoning electronics industry had made great strides since the late 1950’s, offering components of both greater reliability and lower cost. Bosch took full advantage of the improving technology. Their new Jetronic system debuted in the autumn of 1967 on the Volkswagen 1600 LE and TLE. In the next few years, it was offered by Citroën, Mercedes-Benz, Saab, Volvo and others.

1968 Volkswagen 1600 TLE with Bosche Jetronic ECU.

The Jetronic system housed its seven discrete transistors and associated components on a single circuit board inside a metal o-ring-sealed Electronic Control Unit (ECU), slightly smaller than a tissue box. Like the Electrojector system, it utilized solenoid-operated injectors, low-pressure injection into the intake ports, and a continuous-circulation fuel loop. Fuel injection quantity was varied by modulating the opening time of the injectors. This was determined by the ECU based on manifold vacuum, inlet air temperature, engine temperature, engine speed, atmospheric pressure (thus offering automatic altitude correction) and throttle position.

Drivability of the Jetronic was very well received; power output was comparable to multiple carburetion; exhaust emissions were decreased and fuel consumption was drastically reduced in city driving due to complete fuel-feed cut-off on deceleration above 1200 rpm.

Electronic fuel injection soon became near ubiquitous, and in 1979 Bosch introduced their Motronic system on the BMW 732i. Motronic added active ignition timing to the duties of the fuel injection ECU, setting the stage for total electronic engine management systems.

Ever more powerful and compact semiconductor electronics along with digitalization allowed for the introduction of anti-lock braking systems, stability control, voice activation and recognition, navigation systems, active cruise control and various other driving assists.