A SURVEY OF EARLY POWER TRANSISTORS

by Joe A. Knight

SYLVANIA 1950s GERMANIUM POWER TRANSISTORS

ABOVE, L-to-R: It would seem that Sylvania's use of rather thin wire leads in their Germanium Power Transistors was a limiting factor in their first generation 1954 "2N68/2N95" design. By early 1955 they had released the PNP type "2N68H" (the first item) and the NPN type "2N95H" (the fourth item), with the early style color lettering and now using stiff heavy gold plated wire leads. Plus, a new internal construction, seen in the cut-open middle item (looking similar to the early CBS types), uses an all-steel 2-part enclosure now placed inside the aluminum cooling fins. These "higher" better built devices could now provide more current capacity in line with Sylvania's ads promoting 'higher current gains' being shown in mid-1955. The same 2.5 watt dissipation rating was unchanged, indicating a likely more efficient design overall. The newer white lettered devices, the 2N68 (the second item) and the 2N95 (the last item), became the norm sometime later in 1955 for this series. There were other later markings of these two devices, usually in smaller white type with date codes and a Sylvania logo.

 

ABOVE, L-to-R: By late 1954 Sylvania came out with two new Germanium Power Transistors, a PNP type "2N101" and a NPN type "2N102" (first item), rated at just 1 watt of dissipation in free air. As can be seen in the second cut-open item these later shown versions look similar to the insides of the new higher current 2N68/95 series shown previously. The question may arise which new device came first, and could it be that Sylvania was economizing by using the same enclosure for both new series? As it turns out, when the previously shown 2N68 item was opened the steel enclosure was marked '2N101' on the outside, showing they were indeed the same device for both series, only using the external cooling fin to allow for more heat dissipation and current gain. By early 1956, Sylvania released another set of Germanium Power Transistors, called the 2N141-144 series. The "2N141" (PNP type), the third item shown and the "2N142" (NPN type), the fourth item, were now rated at just 1.5 watts of free-air dissipation with the external aluminum cooling fins. Their 'naked' counterparts, the "2N143" (PNP type), the fifth item and the "2N144" (NPN type), the last item shown, were rated at 1 watt, with no cooling fins. No doubt there were only two different devices (PNP and NPN) used for this series - along with and without external cooling. Thusly, by early 1956, Sylvania had in their semiconductor inventory a total of 8 different Power Transistor devices available to designers and product manufacturers just before the breakthrough of the TO-3 and TO-6 series in mid-1956. Note: The last item is actually a type "2N144/13", an unusual device listed in the substitution guides. It's not known what the suffix stands for (any guesses?) The split-shell construction is similar to the later CBS "LT5XXX" series (of early 1960's vintage), which were mostly second-source items of earlier devices, like the 2N156/2N158 and 2N101/2N102 types.

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Joe A. Knight Early Power Transistor History SYLVANIA Page 3