EEVblog #709 – EDC 4601 AC Voltage Standard Teardown

Dave does some performance checks and then tears down a Krohn Hite EDC 4601 0.05% 6 decade 1ppm resolution 0-1000V AC voltage standard.

Service Manual with schematics

MV106 DC Voltage Standard

User manual

XR2228 Multiplier/Decoder
Epson SPG8640 oscillator/divider

Forum HERE

Hires teardown photos:

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    • tlhIngan

      The standby/operate switch is a neat safety feature – changing the ranges puts it in standby mode so you don’t fry you or your circuit if the range switch is accidentally touched. (Yes, you can kill yourself with a 9V battery, so even the 10V range is potentially lethal).

      That is rather good design.

      Though, why light bulbs and not LEDs? I know lightbulbs are old school, but LEDs would serve the purpose far better in such a modern piece of test equipment. Especially since there are LEDs elsewhere in the instrument.

      Yes, I can imagine it hums at 1kHz since that’s close to peak sensitivity for most humans.

    • John Senchak

      Vactrol porn

    • Synthetase

      Fascinating video, Dave.

      Vactrols are still heavily used in guitar amps for channel switching or effects (amplitude modulation, etc). You can make your own using an LED, an LDR and some heatshrink tubing.

      As for the device itself, I assume that it uses a sinewave oscillator to produce the frequency required and then amplifies it (hence the power amp at the back), but how does it get 1000V from that low voltage split supply?

    • blipton

      Is this only intended to be used as a reference, or can it actually be used to power a load?

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