A

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The Tektronix Type A is a single-channel preamp introduced in 1954 for 500-series scopes. It provides two inputs and has a switch to select between them. A 545 with a Type A has a system risetime of 18 nanoseconds and a bandwidth of 20 MHz. It was designed by Bill Polits.

Although 1959 was the first year one could find a "Type A" in the catalog, the same instrument with earlier "Type 53/54A" nomenclature was in the August 1956 Short Form catalog, and its Type 53A ancestor was in the August 1954 catalog which introduced the first 500-series scopes, the 531 and the 535.

Type A was the first letter-series plug-in to be discontinued, in 1962. Customers were told to get Type B instead, although it cost more.

Key Specifications

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Bandwidth is 10 MHz in the 530 mainframes.

Catalogs don't list 53A performance in the 540 mainframes. The Factory Cal Procedure says 20 MHz, but this is wrong. (A Type 53A's measured 3 dB point was around 17 MHz while a Type A made 23 MHz. Furthermore, the front-panel artwork reads ".017 usec" for 53A and .015 for A.)

Internals

Type 53A has only three tubes, and no T-coils.

The plug-in uses a 12AU6 in the front end as a cathode follower. This input stage drives the second stage, a differential amplifier made of two more 12AU6 tubes.

The second stage drives the output stage, a pair of cathode followers made of both halves of a 12AT7 tube. The plate of each output tube is connected to the cathode of the other output tube by a 5 nF capacitor. This "cross-bootstrapping" extends the high-frequency response.

Pictures

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  53A front

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  53A chassis

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  53A chassis bottom

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  53/54A front

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  53/54A top (dirty, missing two tubes)

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  53/54A bottom

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  53/54A left

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  53/54A rear

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  Type A front

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  schematic