The Tektronix Type 1A6 is a low-cost differential plug-in for 500-series scopes.
A replacement for Type D, it senses down to 1 mV/div at 2 MHz bandwidth, with 10,000-to-1 common-mode rejection to 100kHz and +/-15V common-mode range.
The 1A6 was designed by technician Vaughn Weidel, based on Type 1A7. The input stage is a matched pair of 8393 Nuvistors, and the front panel is styled like Type 1A5. Unlike Types W and 1A7, Type 1A6 was never converted to FET input.