by Joe Knight





Shown above is a BTL Type A point-contact cartridge transistor with the distinctive splayed connecting pins. Wax was used inside the cartridge to provide some form of moisture protection - NOT!  Few of these first ones performed longer than a few weeks or months.


With the widespread availability of the BTL Type A transistor within the telephone, military and defense communities, immediate efforts were begun to find it's potential for 'power' amplification. It was soon acknowledged that point-contact transistors would only achieve 50-75 milliwatts of power due to their limited current passage. While this was just enough for driving small radio speakers it was not enough to provide the true power amplification and circuit control needed for larger semiconductor applications. It wasn't until the development of the first junction transistors in 1951 that Bell Labs could see the prospects of true power transistor devices capable of one or more watts of dissipated power. In Class A circuits this would result in almost 1/2 watt of power output. Thus, in 1952, this 'one+'  watt dissipation level was considered the bar to attain for Power Transistor status by BTL and most of the other major semiconductor labs, including RCA, GE, Westinghouse and others.


In attempts to gain further power from the Type A transistor BTL experimented in 1951 with adding external radial cooling fins to the shell. This did permit stable thermal conditions of up to 200 mw of power. External heat-sink designs have become common place for transistor applications ever since, often giving 2-3 times the dissipation potential over normal open-air usage.





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Joe Knight Early Power Transistor History – BTL/WESTERN ELECTRIC  Page 2