Measuring High Voltage power supply

Did you read disclaimer ? Then let’s go.

Remember !

There are 2 voltages to check, since this is common failure. Using a high voltage probe you can read directly 1.5kV for one of them, and with the max hold feature of your multimeter almost 6kV for the other one.

Do not use any multimeter directly: this operation can/will kill it and/or the power supply itself.

Yet, with your multimeter (check it supports 1kV !), you can measure AC output of transformer: expecting 610VAC, or 590VAC (see service data, main page). But this part never fails.

Note: 610*sqrt(2)*2200/(2200+330)*8 = 6kV

EHT wiring diagram
HT probe Metrix HA 0794 990MOhm
High voltage for treble panel: almost 1.5kV
High voltage for bass panels: almost 6kV

Note the division ratio: (10/(990+10))=1/100

You will never measure 6kV: even 1000 MOhm is already too much load. Thus, use MAX feature on your multimeter, as it is the case here in illustrations. For the lower 1.5kV, you can read directly without using the MAX feature.

You will measure more on an EHT which is connected to the cells (as above: 5.6kV for example) than on one which is not: expect 5.2kV. If less than 4.6kV (still with MAX feature), check your diodes, in particular reverse current at 1000V (see reparation page).

If your multimeter does not feature MAX function, then measuring as low as 4.7kV with a 1GOhm probe is normal.

In these pictures, power supply is already a custom re-built one and bulgin power plug was replaced by a modern IEC one.

Alternative (simple) check: measure impedance

Provided the power supply is off for more than 2 hours, you can check resistance and capacitance between the 4 pins. You may have to unsolder wires first.


  • GND vs 1.5kV: 10nF (normal !)
  • GND vs 6kV: 2.7nF
  • 1.5kV vs 6kV: 3.55nF

resistance: negative probe on ground

  • VAC: 2.5MOhm (normal !)
  • 1.5kV: >500MOhm
  • 6kV: >500MOhm

resistance: positive probe on ground (diodes are passing)

  • VAC: 2.5MOhm (normal !)
  • 1.5kV: 8MOhm
  • 6kV: 88MOhm

And 1.5kV vs 6kV: 42MOhm

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