by Joe A. Knight



ABOVE, L-to-R: To this end several of the major radio parts and radio manufacturers had undertaken major power transistor development programs to see who could be the first to market with these much needed devices. Motorola, having already been a car radio manufacturer, was heavily committed to this endeavor. They had developed in 1955, according to their own literature, the first triangle shaped mounting design we now call the TO-3 type (shown above). The first two transistors, the "XN10" and its cut-open version, were likely the first developmental type built along these lines by late 1955. Motorola was also manufacturing in 1955 an in-house TO-3 power transistor version called the "2NJ4" (likely similar to the XN10 device) for use in their two-ray radios. By mid-1956 Motorola was producing their new RETMA registered TO-3 output series, the 2N176 (far right two items), the 2N177, 2N178 and 2N179. The 2N176 and 2N178 power transistors were the ones most useful in the car radio chassis' for the next new model year 1957 autos. Most new transistorized car radios were then using the hybrid design by just using power transistors in the output stage and vacuum tubes in the other stages. The type 2N176 design was licensed to other manufacturers and is likely the all-time sales leading output device for the 50's and 60's.


In 1957 Motorola came out with another TO-3 series (not shown), the 2N350, 2N351 and 2N350A. And in 1958, they released more TO-3 types (not shown), the 2N555 and 2N618. Motorola also second sourced the Delco TO-6 type "2N174" power transistor and even went on to develop a "low silhouette" version of it in 1960 called a TO-36 type. Motorola also later developed low profile versions of their own TO-3 types. Still today, Motorola is a leading producer of popularly used solid state output devices in audio equipment and other electronic systems.














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Joe A. Knight Early Power Transistor History MOTOROLA Page 2