The Tektronix 175, introduced in 1961, is an external unit that extends the current capability of the 575 curve tracer. The 175 uses the standard circuit topology for the collector supply: a variac followed by a multi-tap isolation transformer, followed by full-wave rectifiers.
There are two modes:
- 0 - 20 V collector voltage, 200 A maximum collector current
- 0 - 100 V collector voltage, 40 A maximum collector current
Separate transformer taps and rectifiers are used for the two modes. In the 0-20 V mode, 45L10 rectifiers are used. Unlike the 575, which routes the test current through the front panel switches, the 175 routes the 0-20 V collector supply through 100 A relays, whose coil current are switched by the front panel (i.e., the "COLLECTOR POLARITY" and "TRANSISTOR SELECTOR") controls. Otherwise, the front panel switches would have to handle high currents and would be massive and difficult to operate. The front panel switches are break-before-make, which is important because if the relay coils were to be energized in the wrong combination, a short circuit would be formed. In the 0-100 V mode, the test current flows through the front panel switch.
The Tektronix 175 requires a 575 to work, which provides +300 V, +100 V, and -150 V to power the step generator circuit in the 175. The cable that connects the 175 to the 575 uses Amphenol 165-14 and 165-15 connectors.
The front panel of the 175 has Superior Electric Supercon connectors for the high-current measurements. The positive (red) plug that goes into the 175 is a model PP100GR pin plug. The negative (black) plug that goes into the 175 is a model PS100GB socket plug.
The 175 is 12"x13"x24" and weighs 38 kg (84 pounds). Most of the weight of the 175 is due to the large transformer (part number 120-197) for the collector supply.