59
The Tektronix Type 59 is a 400 kHz amplifier for 560-series scopes. It was introduced in 1961, and at $50, it was the lowest-priced plug-in in 560 series.
It does not have a calibrated input attenuator. The input takes banana plugs.
<gallery> Image:Tek type 59.jpg|From 1961 catalog </gallry>