A SURVEY OF EARLY POWER TRANSISTORS by Joe Knight THE POWER TRANSISTOR BELL TELEPHONE LABS AND WESTERN ELECTRIC
While the previously mentioned W.E. 2N66 Power Transistor was undergoing final development, Bell Labs worked on a similar device for use within the telephone system but strictly for audio-frequency applications. This device became the W.E. 6A PNP Germanium Alloy Power Transistor but with about 2 watts of dissipated power. It first came out in 1955 with BTL releasing the first 6A data sheet as "Issue 1" on September 16, 1955. (Historically, BTL data sheet releases always lagged behind actual device production by weeks or even months.)
The above photo shows on the upper left an early pre-production 6A type in a rounded dome can with an exhaust tip on top, likely from early 1955. The 6A Power Transistor on the right, from early 1956, is a regular finished product. The above lower cut-open 6A shows the similar, but larger germanium pellet mounting pillar and thicker collector lead, which allowed for greater power dissipation than the 2N66. This new transistor housing design (shown at far right) also had a bottom threaded bolt mounting, as shown below, for better heat-sink conductivity.  This new basing configuration would be common for many more of the new W.E. Power Transistors to come and became the RETMA standard 'TO-32' base. Go To BTL/Western Electric Early Power Transistors, Page 12
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