We have two of these 3A74 mod 505 plug-ins at the museum but cannot find any information on them in the microfiche. It has several interesting features such as no model number, serial number, or Tektronix logo on the front, no inputs, no mode switch, and a "vertical or horizontal" legend. It does show remnants of a label on the front.

The internal construction shows the inputs wired to the rear connector.

The tag indicates it is Mod 505 and has a serial number of 000280. This was likely the running SN for the Type 3A74 standard plug-in.

This photo shows the simplification when compared to the standard Type 3A74 plug-in. Another interesting feature is the 1-2-4-8 control instead of the more standard 1-2-5.

Let the museum know if you have any information on the Mod 505 Type 3A74 plug-in.