282
The Tektronix Type 282 is an active adapter introduced in 1966 that allows high-impedance probes to be used with instruments that have 50-ohm inputs. It is a unity-gain buffer with an input impedance of 1 megohm in parallel with 16.5 picofarads and a low output impedance. The high-impedance input stage is a dual-JFET where one transistor operates as a source-follower and the other transistor operates as a current source biased with Vgs=0. The risetime is 3ns when driven from a 25-ohm source.