If you get the "Sorry, the file cannot be displayed. There seems to be a technical issue ..." error when trying to view an image, a workaround is to click on the cog icon in the upper right side of the media viewer, and then select "Disable Media Viewer". We are aware of the problem and are looking for a solution.
The Tektronix 3A1S is a vertical plug-in for the 561S. It is specified to have an input impedance of 47pF in parallel with 1 megohm. Input sensitivity in a 561S is from 10mV/div to 10V/div. Risetime is specified to be 14ns, giving a -3dB frequency of 25MHz. The input signal passes through a compensated attenuator switch and then into a 7586 cathode-follower biased with 2mA plate current.