The Tektronix Type 1A1 plug-in for the 500-series scopes has two channels and a -3 dB point of 50 MHz at 50 mV/Div, 28 MHz at 5 mV/Div, and 2 Hz to 15 MHz at 500 μV/Div when channels 1 and 2 are cascaded.
Early production used a Nuvistor front-end, and rotary input switches that were concentric with the BNC jacks, while later units have FETs and lever switches. Type 1A1 uses the "ALT SWEEP SLAVE PULSE" signal that is sent by scopes on pin 7 of the plug-in connector. In a Type 547 mainframe, this signal allows channel 1 to be displayed using the "A" timebase and channel 2 using the "B" timebase. This is useful, for example, to view the IF and AF of a radio receiver at the same time. Even after the front-end transitioned from Nuvistors to FETs, the output amplifier continued to use Nuvistors.
Types 1A1 and 1A2 were introduced together in 1964, the former for high-end use, the latter as an upgrade/replacement for Type CA. Both remained available until the 500-series scope line was discontinued after 1974.
The 1A1 may have evolved from the Type J, which never went into production.
Tektronix' German distributor, Rohde & Schwarz, apparently manufactured a version of the 1A1 in Germany (see Links).
- 1A1 @ amplifier.cd (pictures of a German-produced 1A1)