A SURVEY OF EARLY POWER TRANSISTORS

by Joe A. Knight

MALLORY 1950s GERMANIUM POWER TRANSISTORS

 

This covers the power transistor line made by the P.R. Mallory Co. and herein after referred to as "Mallory".  Mallory had long been in the radio parts business since the late 1920's and had been a major capacitor/condenser manufacturer for many years.  Likely wanting to expand their product line into power supply semiconductor devices, which their competition was already coming out with by the mid-50's, Mallory began their research into producing their own Germanium power transistors sometime in late-1954/early-1955.  By the end of 1955 they were in 'pilot-plant' production (announcement in 'Electronics', February, 1956) with their own 440-, 441- and 442-series transistors.  These were available for $12.50 each in lots of 50 or more. Mallory was one of those semiconductor manufacturers which never delved into making small-signal devices - only the larger high power types.

 

ABOVE, L-to-R:   The second shown device, the "255", is likely one of Mallory's first PNP germanium power devices (still works), built on a large bent copper strip, possibly made in the '25th week of 1955' (if the number is a date-code?).  Coincidentally, this type of construction looks very similar in design to the Transistor Products "X-78" power transistor first commercially produced in early 1954.  However, this Mallory device was built on a larger scale to allow for much more heat dissipation as required of a true high power transistor.  The first shown device by Mallory appears to be a similar PNP germanium device, only more compact and now on a bent steel strip.  This device combination seems the likely predecessor in the final design of their 440, 441 and 442 series transistors as they are all mounted on steel bases and similar in element size.  The middle item shows the interior of these devices, a "441", in a large base design.  The fourth item is a Mallory "441" in a small steel base and small cover configuration, although this may correctly be a "442" type (see photo on Page 2).  The far right item shows an interior of the previous type and also looks similar to the transistor element mounts press-fitted into the larger heat-sinks shown on Page 2.

 

All Mallory power transistors appear to use the same Germanium element size and construction and while the electrical characteristics did vary with each series, another major difference was the size of the base or the heat-sink associated with individual units.  The 440 series came as a "440-C-C" (also RTMA registered as a 2N151) and as a "440-C-E", both rated at 5 watts of dissipation.  The 441 series, similar to the 440 series, came as a "441-C-C" and as a "441-C-E", both rated at 15 watts of heat dissipation.  In both these series the "C-C" devices came in a large 2" long radial-fin heat sink (see Page 2) and the "C-E" devices came in a large 1 3/8" flat steel base like the middle item above.  Finally, the 442 (also RTMA registered as a 2N154) series came as a "442-C-A" (built like the fourth item above, small enclosure), rated at 1 3/8 watts dissipation, and as a "442-C-D", rated at 2.75 watts and built with a  1" long radial-fin heat sink, as in the middle item on Page 2.

 

Go To Mallory Early Power Transistors, Page 2

 

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Joe A. Knight Early Power Transistor History – MALLORY