The Tektronix 1A2 is a two-channel plug-in amplifier for 500-series scopes. It provides a -3dB point of 50MHz in a 544, 546, or 547. It uses a 7586 nuvistor at the front end as a cathode follower. Then one input of an NPN differential amplifier is driven to produce a differential current-mode signal at the collectors. Silicon diodes form an analog multiplexer that switches between the two inputs. A cross-coupled pair of PNP transistors forms a multivibrator that generates the voltages that control the diodes that select the input channel.