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.
There were three distinct versions of 1A1.
- The first version, from 1964 to 1966, has a Nuvistor front-end, and rotary input switches that were concentric with the BNC jacks. The knobs to invert the input channels are concentric with the vertical position knobs.
- The second version, from 1966 to ??? has fluted round V/cm knobs, and lever switches. The channel inversion control is an organ-style pull-push knob.
- The third model, from ??? until the end has four-sided V/cm knobs and a FET front-end.
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.
Type 1A1 has an External Trigger output for mainframes prior to the 547 that don't support plug-in triggering.
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.
The 1A1 is not a perfect superset of the 1A2; it supplies external trigger from channel 1 only.
The 1A1 may have evolved from the Type J, which never went into production.
556 with second version 1A1 in left bay and first version 1A1 in right bay.