420

Manuals – Specifications – Links – Pictures

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.

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).

Internals

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..

Pictures

• 

  Entry in 1950 Catalog

• 

  later model 420 (with 13 and 6 kV outputs) in a 517

• 

  Schematic of 420 (to the right of and including the transformers) in the Type 517

• 

  Schematic of 420 (between the dashed lines) in the Type 507

• 

  Five 1X2 high voltage rectifier tubes inside a 420A

• 

  HV multiplier, "black beauty" capacitors inside a 420A

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