The Tektronix 420 is a high-voltage power supply used in the Type 507 and Type 517 scopes. It contains transformers, rectifier tubes and filter capacitors in a separate, oil-filled enclosure with ceramic output feed-through posts.

Tektronix 420
high-voltage power supply
420 internal view

Produced from 1950 to (?)

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(All manuals in PDF format unless noted otherwise)

Key Specifications

Outputs +20 kV @ 200 μA / –4 kV @ 700 μA, or +10 kV @ 400 μA / –4 kV @ 1.4 mA. Later models add +13.3 kV and +6.6 kV output taps (6.6 kV/3.3 kV in reduced output mode).


The HV rectifiers are five 1X2 tubes, one for the negative and four in a Cockroft-Walton quadrupler circuit for the positive outputs. To accommodate the switchable output voltage, rectifier heaters are supplied from a second transformer inside the 420.

The transformers are driven by independent oscillators using tubes located on the mainframe chassis, a 6AU5 for HV and a 6AQ5 for heaters.

In the 517, the HV oscillator runs off an unregulated supply through its own DC series regulator with no feedback path from the HV side, only the oscillator input voltage is regulated. The 507 HV oscillator, supplied from the regulated +225 V rail, takes feedback from the negative HV output..


Some Parts Used in the 420

Part Part Number(s) Class Description Used in
1X2 154-0005-00 Vacuum Tube (Diode) high-voltage rectifier 420 507 565