The Tektronix Type 3A1 is a dual-trace amplifier plug-in introduced in 1963 for 560-series oscilloscopes. Bandwidth is 10MHz (35 nanosecond risetime). The input impedance is 47pF. Deflection factor ranges from 10mV/div to 10V/div. The input signal passes through compensated attenuators and then into a cathode-follower stage made of two 7586 Nuvistor tubes. Channel switching in ALTERNATE mode is done using diodes. The output stage that drives the vertical deflection plates of the scope uses a pair of 8233 frame grid power pentode tubes.