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Tektronix Type 81
Plugin Adapter
Type 81 with a 1A2 in a 585A

Compatible with 580-series scopes

Produced from 1960 to 1972


Factory Calibration Procedures

Manuals – Specifications – Links – Pictures

The Tektronix Type 81 is a plug-in adapter so that letter-series and 1-series plug-ins can be used in 580-series scopes.

The 81 and 81A are significantly different. Type 81 is tube-based and has a bandwidth of 33 MHz. Type 81A is solid-state and has a bandwidth of 50 MHz. The 81A was designed by John Gates.


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The Type 81 contains a two-stage amplifier. The letter-series plug-in drives the input stage of the Type 81 which is high impedance (grids of a 6GM8 stage with T-coil peaking) so that the plug-in sees conditions similar to the input of a 530-, 540-, or 550-series scope. The second stage is a 6DJ8 cathode-follower, which drives the 580-series scope's 93 Ω input impedance. Type 81 also terminates the grid line of the distributed vertical amplifier (delay line driver).

Type 81A has a FET source follower pair followed by cascoded BJT amplifiers.

The Type 81 does not have a spoiler switch. The Type 81A has a spoiler switch.


Type 81

Type 81A