551

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The Tektronix Type 551, introduced in 1958, is a 27MHz dual-beam scope that takes two letter-series and 1-series plug-ins. Unlike the 555, it has only one set of horizontal deflection plates and the trigger and sweep circuitry are built in to the mainframe. Like the 555, the 551 has an external power supply unit. The external power supplies of the 555 and 551 are not interchangeable. The vertical amplifiers of the 545A, 551, and 555 are identical.

The 551 uses an L-C delay line for each vertical channel.

A factory modification, MOD 108A, was available for increasing the CRT acceleration voltage from 10kV to 12kV. This improved trace visibility at high sweep rates.

Early 551 units used UHF connectors. Many were converted in the field to use BNC connectors.

Comparison of 551 with 555
551 555
Risetime with Type K 14ns 12ns
Acceleration Voltage 10kV 10kV
Price in 1965 $1850 $2650
Indicator Weight 52 pounds 68 pounds
Power Supply Weight 42 pounds 45 pounds
Power Consumption 850 watts 1050 watts