by Joe A. Knight



The Motorola, Inc., and Motorola Semiconductor Products Div., both makers of transistor products at different times in the company history, are hereafter referred to as "Motorola".  They began their early research into transistor products likely by 1952 and had experimented with Point-Contact types in 1953, producing one such device called the "EP-7".  By late 1954 Motorola was producing their own in-house line of transistors which by 1955 were being used in their new VHF two-way radios, a pocket pager, and a power-line carrier system.  Their early developmental junction transistors carried an    "XN __" designation, while in-house production junction transistors were identified as a "2NJ___" series (likely the "J" standing for a Junction device).  These items did not correspond to any RETMA registered semiconductor devices or numbers.



ABOVE, L-to-R:   By early 1955 Motorola had developed two large prototype Germanium alloy-junction  power transistors, one in a blue painted brass enclosure (far left) and one in a black painted brass enclosure (far right).  Almost every one of these has a different series of control numbers and letters stamped on the bottom brass bolt face.  However, their meaning is not clear at this time.  Neither is the meaning of the identifying two colors.  It might possibly indicate a production line test limit for higher or lower gain units.  The middle device, showing the interior construction of a blue type device, looks identical inside to the black type device.  Their likely rated power is about 5-7 watts dissipation as this element design was the prelude to the next generation of TO-3 devices, usually power rated at 8-10 watts of dissipation early on.  As 1955 came to a close several manufacturers were all working on their next generation of output devices that could be marketed for use in the blossoming car radio market.  In the mid-fifties not everyone ordered their new auto with a radio as it was not an inexpensive option back then.  But, as the American economy grew more and as the public buying tastes also grew, more and more car buyers came to expect the latest convenience items in their flashy new Detroit vehicles.  However, automobile tube radios were big, heavy and hot and meant a lot of service headaches for the dealers and owners.  If transistors could be developed that would make the car radios more economical, more efficient and less problematic then everyone would be a winner.





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Joe A. Knight Early Power Transistor History – MOTOROLA