Type 1A6 is a low-cost differential plugin for 500-series scopes.
A replacement for Type D, it senses down to 1mV/div at
2MHz bandwidth, with 10,000 to 1 common-mode rejection.
Type 1A6 was introduced in 1967 or 1968, and was dropped after 1973.
Not as many units were sold as the more sensitive Type 1A7 or
the faster Type 1A5.