661

The Type 661 is a sampling scope made by Tektronix in the 1960's. It accepts two plug-ins: a sampling unit and a timing unit. At least two sampling units were made, the 4S1 (1GHz) and the 4S2 (3.9GHz). At least two timing units were made, the 5T1 and the 5T3. These timing units use tunnel diode triggering. Two coaxial cables in the scope connect the sampling and timing units. One cable sends the trigger pickoff signal from the sampling unit to the timing unit. The other cable sends the timing ramp from the timing unit to the sampling unit.