175

The Tektronix 175, introduced in 1961, is an external unit that extends the current capability of the 575. The 175 uses the standard circuit topology for the collector supply: a variac followed by a multitap isolation transformer, followed by full-wave rectifiers.

There are two modes:

• 0 - 20V collector voltage, 200A maximum collector current
• 0 - 100V collector voltage, 40A maximum collector current

Separate transformer taps and rectifiers are used for the two modes. In the 0-20V mode, 45L10 rectifiers are used. Unlike the 575 which routes the test current through the front panel switches, the 175 routes the 0-20V collector supply through 100A 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 0-100V mode, the test current flows through the front panel switch.

The Tektronix 175 requires a 575. The 575 provides +300V, +100V, and -150V to the 175, which power the step generator circuit in the 175.

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.

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  Front

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  Front

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  Left

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  Left internals

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  Right

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  Right internals

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  Rear

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  Step amp

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  Switching diagram

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  Collector sweep

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  Bottom view

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  Left internal

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