1957 · Transistor Curve Tracer · Work 831 of 1,871
A measuring instrument in the test laboratory of a semiconductor factory, a tall cabinet with a light grey-blue front of plain smooth panels standing on a steel table and turned at a steep slant, in its upper left a round screen thirteen centimetres across glowing with a family of green curves stacked one above another, beside it two large black knobs, at its foot a protruding test drawer with two rows of sockets holding a single small transistor in a metal cap, a hand in a white coat sleeve holding the next one in tweezers, shallow wooden trays with sorted transistors in three heaps, fluorescent light from above.
What it was used for
The Tektronix Type 575 drew families of semiconductor characteristic curves on a screen: current against voltage, in steps of base current. Pass/fail tests were possible with it, and according to a technical article on using the instrument the mode of failure could often be determined as well - an open device as a horizontal line at zero current, a shorted one as curves nearly vertical at near-zero voltage, a sloping straight line pointing to a resistive fault. It also showed the minimum current that still provides adequate current gain. The collector sweep reached 200 volts at up to 1 ampere, or 20 volts at up to 20 amperes, that is 400 watts of test power; vertical deflection ran from 0.01 mA per division to 1 A per division in 16 steps. The instrument weighed about 30 kilograms.
What was new
The method itself was taken over from tube measurement: Tekwiki lists the Type 570 of 1955 as Tektronix's first curve tracer, a vacuum-tube instrument that swept the plate voltage from zero to a selectable maximum while stepping the control grid. The 575 of March 1957 applied the same to transistors, with base-current steps instead of grid-voltage steps and collector currents up into the ampere range; it could also display base voltage on the vertical axis. The 1959 catalogue price was $975, that of the tube instrument $995. The instrument found a second career: an article by Dennis Feucht recommends the long-discontinued 575 as a low-cost surplus tracer for power semiconductors - Darlingtons, diodes, MOSFETs, IGBTs - although it was designed for bipolar transistors.
What the sources leave open: For that second career the step generator no longer sufficed: it was limited to 12 steps and at most 0.2 V per step, too little for most FETs; as a workaround a resistor went between the base and emitter terminals, and at 2 V per step three or four curves then typically appeared. Milliamperes per base step, unit numbers and any named user company are not documented; the 1957 Tektronix catalogue page was unreachable. Feucht's article is undated.