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EARLY TRANSISTOR HISTORY AT MOTOROLA “THE EARLY YEARS” By Ralph Greenburg |
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The Physics guys and Chemists knew how to make the devices from growing the germanium ingots to packaging the die in small metal cases. It was applications job to do all the electrical evaluation and figure out the transistors performed in simple circuits. We were also called upon to improve the speed controls of the apparatus used to pull the ingots and to modify the temperature controllers that were used in alloying the Indium pellets into the Germanium die.
As long as we were working with small signal devices the purchased power supplies, signal generators and multi-meters tat allowed us to evaluate parameters and create basic circuits. Also there were no problems with supplies of resistors and capacitors but the transformers and inductors that matched the low impedance of transistors were virtually non-existent. However with the help of the Radio Amateur Handbook and other reference material we were able to hand wind these components. One time one of the engineers needed a very high Q coil for a circuit he had designed and the equations in the had books informed him that the coil had to be 1/4 “ long with a 3” diameter. There was no coil form like that in the lab but one of technicians said, “I’ve got just the thing, I’ll bring it in tomorrow.” It was “just the thing”, an empty oatmeal box.
The characteristics of the XN1 were all over the map with current gains varying from 5 to 100 and frequency cutoff from 100khz to 1mhz. So we would sort the wheat from the chaff and find devices that would perform well in a number of basic circuits. One day an engineer decided he could find enough good transistors to make a super-heterodyne AM radio and he did. We all gathered around and could faintly hear KOY. KOY was the first station in Phoenix and at 550khz had the strongest signal. The engineer decided the low volume was due to poor reception inside the lab. He took the radio outside and with a 50 foot antenna the reception was loud ad clear for about 2 minutes. Then all we heard was shrill noise. What had happened?
Since we knew the germanium transistor had degraded performance at high temperatures and since the lab was a comfortable 75 degrees as compared to the August heat of Phoenix above 110 degrees we had discovered thermal run-away. We didn’t know it was thermal runaway until we found an article in either a Philco or a Bell Lab technical bulletin. The author even explained how to modify circuits to eliminate the effect.
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A Transistor Museum™ History of Transistors Publication COPYRIGHT © 2008 by Jack Ward. All Rights Reserved. http://www.transistormuseum.com/ PAGE 2 |