A SURVEY OF EARLY POWER TRANSISTORS by Joe A. Knight RCA 1950s/60s GERMANIUM POWER TRANSISTORS
ABOVE, L-to-R:   It seems that RCA developed the 'cup' design into something next identified as the black colored "SX 150" (first item), likely in late 1953. This was a PNP Germanium device and was constructed with a threaded stud on the bottom for attachment to a heat sink for even higher wattage dissipation. The next item is the white colored "SX 150A", from early 1954, with likely better element design for more power. The junction elements are now mounted on a heavy copper base.  It would appear that RCA used this device in their first experimental automobile receiver (see RCA Industry Service Bulletin LB-958, August, 1954 or "Transistor I", RCA, 1956).  The first  photo below shows two large white output devices just to the left of the output transformer.  These appear to have the same "H-" number series as on top of the example above and are mounted using the same stud attachment.  The middle black colored device, a "SX 155A", is a PNP Germanium type and dated 1955.  The predecessor to this one, the "SX 155", was used in two experimental transistor amplifiers made by RCA in 1955, one a 5-watt design and one a 20-watt design.  The second photo below clearly shows the SX 155 in the 5 watt amp used in a push-pull Class B output design.  Coincidentally, both these output devices look very similar to the W.E. 2N66 power transistor which also came out in 1955.  The forth device above, a cut-open "TA-1621" (dated 6-23-56), is a major shift in the RCA power transistor basing, doing away with the stud mounting and inside looking similar to other manufacturers classic TO-3 Germanium element designs but in an all copper housing.  The last item is another very similar device, a "TA-1621A" (dated 7-15-56).  Both last two transistors have three short pins on the bottom, similar to the Clevite type "CTP 1002" from early 1956.
ABOVE:  RCA "SX 150A"  used in Experimental Automobile receiver in p-p output.		ABOVE:  RCA "SX 155" used in experimental 5 watt p-p amp.
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