556

The Tektronix 556 is a dual-beam scope, the successor to the Tektronix 555. It is a one-piece unit. Triggering and sweep circuitry is integrated into the 556 mainframe, as opposed to the removable timing units in the 555. The 556 takes two letter-series or 1-series vertical plug-ins. The bandwidth is 50MHz.

The 556 is a true dual-beam scope and none of the signal paths are shared between the two beams. Electrically speaking, the power supply and the calibrator are the only parts that are common to both beams. Apart from the power supply, the 556 has almost complete left-right symmetry, corresponding to top and bottom beams. Although the beams can be operated completely independently, the 556 provides many options for routing signals between the vertical plug-ins, triggers, sweeps, horizontal amplifiers, and vertical amplifiers. For example, a common use for a dual-beam scope is to view two simultaneous single-shot events, both sweeps being triggered by one of the traces. For this purpose, the 556 allows the output of one sweep generator to be routed to the horizontal amplifier of the other beam, so it drives both beams. Many other more sophisticated modes are also available. The triggering in the 556 is done using tunnel diodes and the trigger circuit sits on its own small PC board just behind the trigger source selection switch.

A rack-mount version, the RM556 also exists.

The 556 superficially resembles the 565, which is is also a dual-beam one-piece scope, but the 565 takes two 2-series or 3-series vertical plug-ins and has much lower vertical and trigger bandwidth.

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  Front view of an RM556.

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  Trigger board contains two tunnel diodes and a reed relay.

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  Top view.

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  Output amplifier driving deflection plates.

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  Neck of 556 CRT. The tube contains two electrically independent guns and vertical and horizontal deflection plates.