EEVblog #709 - EDC 4601 AC Voltage Standard Teardown

[funkyant]

You're kidding right?
This is your example of the quality difference you are complaining about? Seriously? 

loooooool 

[TheRuler8510]

Anybody know what the 4601 AC voltage standard is worth?

I picked one up recently cheap and I'm wondering if it is worth selling or if I should keep it. None have appeared on eBay in a while.

Regards,

[BrianHG]

Correction on vactrol datasheet, this is the actual part used in the EDC 4601 AC Voltage Standard:

http://www.excelitas.com/downloads/dts_vtl5c2232.pdf

That center tap is crucial if you want to correct for the ageing of the led, photocell & if you want to perfectly match multiple vactrols.

I used to use these for an stereo audio pre-amp electronic volume control.  The LED current to output resistance generated a nice clean curve.  The photo resistor element responds exactly like a clean noise free, 2 matched variable resistors pots with a center tap.  The slow response of the photocell filtered out all higher frequency electronic noise from the led.  Though obsolete today, it was still useful around the early 2000s for some niche applications.