An Interview with Ralph Greenburg

 Historic Semiconductor Devices and Applications


Oral History – Ralph Greenburg


I’m very much interested in the 2N176 and related devices.  Please provide as much info as you can. Also, the “Motorola Power Transistor Handbook” is a real classic, and I’d like to capture more information about this book.


As you have noted in your discussions of Motorola power transistors the Motorola Auto Radio group had a vested interest to have a useful power device. By 1954 the auto industry announced it was going to switch from 6-volt batteries to a 12 volt system. I believe all American vehicles made the switch for model year 1956.  The Motorola Two-way radio group also was interested. Both groups wanted to eliminate the Vibrator power pack that was used to convert low voltage dc by chopping it to low voltage ac then transforming to about 300 volts and rectifying back to dc. Not only was this costly but the vibrator had a high failure rate. The auto group really wanted an all transistor 12 volt radio but this was not possible until the late 50”s. Therefore a hybrid approach was conceived.  Tungsol and other vacuum tube producers had developed a set of low voltage tubes suitable for AM radio receivers. These tubes coupled to a transistor power output would make a practical interim solution.


The hybrid approach would not work for the two-way receivers since transistors were not available at the very high frequencies that these used.  The hope here was to eliminate the vibrator with an inverter circuit using a pair of power transistors.  



Oral History – Ralph Greenburg


So both groups were sampled with the prototype stud versions and the auto radio group liked the performance and was able to make experimental models that worked off 12 volts. I don’t believe the two-way group was successful with their approach. However the auto group did not like the configuration of the stud package. They wanted a plug in device. That is when Dale Kelley had his inspiration to develop the diamond shape transistor with the base and emitter pins coming out from the bottom of the case that was connected to the collector. Dale even made the emitter-base spacing so at least for prototype work these would fit into a pair of holes on an 8 pin tube socket. The auto guys were ecstatic and the power device could be mounted directly to the radio’s case that would act as a heat sink.


Well as you know the revolution was started, and it wasn’t long until almost every manufacture who wanted to sell power transistors had signed agreements with Motorola to use what would become the TO-3 outline package. I believe Delco and Westinghouse were the only ones not interested and stayed with stud type packages. Motorola should have dedicated a shrine for Dales’s efforts or at least nominated him for some major award from IEEE. 



Go To Greenburg Oral History, Page 6


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