From TekWiki
Jump to navigation Jump to search
Tektronix 422
15 MHz portable dual-trace scope
Tektronix 422 front

Produced from 1965 to 1975

Manuals – Specifications – Links – Pictures

The Tektronix Type 422 is a 15 MHz portable dual-trace oscilloscope introduced in 1966. It was available with an optional battery back for operation without mains power.

Key Specifications

Bandwidth DC to 15 MHz
Risetime < 23 ns
Sweep 500 ns/div to 0.5 s/div
Input impedance 1 MΩ ±2% // 30 pF
Delay line 150 ns, internal delay line
 Input voltage Max. 300 V combined DC and peak AC
Trigger source CH1 & CH2, CH1, External
Channel isolation 100:1 at 40 KHz
Calibrator ~1 kHz ±20%, 2 V ext jack, 0.2 V internal, square wave
CRT T4220 tube, P31 phosphor, 6 kV acceleration (Post-def 4.9 kV), 8 × 10  graticule, 0.8 cm/div
Operating temperature –15 °C to +55 °C
Power AC PS, 110/115/125 or 210/230/250 VAC ±10%, 45 Hz to 440 Hz, 40 W
AC-DC PS, 92–137 or 184–274 VAC, 45 Hz to 440 Hz, 11.5–35 V DC, 30 W
Dimensions AC PS (H/W/D) 6.75/10.0/17.8 inches, AC-DC PS (H/W/D) 6.75/10.0/20.7 inches


Early versions use an 8056 Nuvistor tube for the front-end cathode follower. Later versions use a FET front end. The 8056 Nuvistor used in the input amplifier of the 422 can be replaced by a MPF102 JFET.

The trigger circuit in the 422 has a trigger amplifier driving a 1N3719 tunnel diode, D375, which acts as a Schmitt trigger. The trigger amplifier has a nonlinear deadband diode circuit in the negative feedback path. What results is high gain for small signals (little or no negative feedback) and low gain for large signals (strong negative feedback). Thus, the signal at the base of Q364 has a limited swing over a wide range of input amplitudes. The collector current of Q364 varies between 0 and 9 mA. Depending on the position of the trigger slope control, higher collector current in Q364 either switches D375 from the low-voltage state to the high-voltage state or from the high-voltage state to the low-voltage state. When D375 transitions from the low-voltage state to the high-voltage state, it produces a current pulse in the primary of transformer T401, which produces a current pulse in the secondary of T401. The secondary of T401 feeds another tunnel diode, D405, and the current pulse switches D405 to the high-voltage state, which starts a sweep.

The 422 uses the T4220 CRT.






Some Parts Used in the 422

Page Class Description Used in
8056 Vacuum Tube (Triode) low-voltage Nuvistor triode 422 502 W 1S1 3A7 3S3 3T4 5T3 10A1
T4220 CRT rectangular 3⅜ × 3⅞ flat-faced CRT 422
ZZ1000 Gas Discharge Tube (Voltage regulator) 81 V voltage reference 129 3B1 422