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.

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[DarkFire]

My guess is that they made (make?) so few of these that there's one chap in the factory who makes them. He's probably a grey-bearded, pipe-smoking eccentric genius who's been employed by EDC for the past 45 years but who they don't dare question or god forbid allow to retire because he's the only one with the green fingers who can hand-make these to 2 x better than the stated precision...

[darrenjacobson]

Well, this just goes to show, if you know what you're doing, you can get anything to work. Whoever put this together (ok it was probably a team of people) really knew how these worked. To be able to recycle old parts and designs by strapping on new technology where needed, that takes skill.

[dwDragon]

When you showed the oscillator board, it was like Wizard of Oz going to color. Can't believe that's in the same product as that tin-plated fiasco of a main board.

[sensecam]

Dave, wonderful nostalgia seeing all the traditional analogue electronics! Very good photography. Keep up the good work. 

[zwz.zdenek]

Dave, anyone, please don't judge things so much by the looks. I can tell you from my experience with repairs that devices fail mostly due to (intentional) poor choice of components; that includes lead-free solder. Some of the worst offenders actually look "highly professional." I have several bird's nests of mine I had made 10-20 years ago still going strong, on duty 24/7!

[LEKProductions]

I use vactrols all the time in my DIY analogue modular synthesizer. Probably have about 30 in there aleady. VTL5C3 are favoured in most applications for the best timing curve, VTL5C4 are usable but a bit slow. The /2 suffix represents dual versions.

[mechadrake]

All these videos with insides of various instruments are very riveting.

[thomascoughran]

Back in the 1960s, my brother, a Ham Radio operator had some surplus aircraft radios that he converted for the ham bands. He powered them with a 24VDC dynamotor. The radio supply output was 400 CPS (Hz). They used 400 Hz so it didn't take so much iron in the transformers. Lower frequency meant more weight which resulted in fewer bombs... :-))

[davidahiwaaynet]

That's a great old hand-built unit. Love it!

[petersage]

9:30 Now I'm confused. You'd think the manual for a transfer standard would be a bit more precise in its unit conversions. Maybe we can chalk that up as a typo?

Did everybody else notice several of the trimmer pots have mid-99 date codes?

[Nexfero]

"The light weight of the unit makes it a desirable laboratory instrument".... hahaha it weighs 40 pounds and its got NE 555 timer at 24:45

[WolfmanDude]

I still use vactrols in some of the stuff I build. They are very useful for gain control in analog circuits because they are super linear and also provide isolation.

[anachrocomputer]

Something to watch out for when using the higher output voltages is the screw-heads on the sides of those 4mm banana plugs. The exposed screw-heads are live! There's a big hazard here if you grab the plug when the voltage is turned on. Those 4mm plugs are best avoided in test gear -- even at low voltages, they run the risk of causing a short-circuit.

[Gin-toki]

I would really like a walkthrough of how this AC Voltage Reference works, perhaps with some state-of-the-art Dave CAD drawings :)

P.S. those Vactrols are frequently used in analog synthesizers for various voltage control of diffrent parameters and they are stil manufactured :)

[bytefree]

they are planar mosftes I believe. Top quality.

[DjVortex-w]

I have never quite understood the "don't turn it on" part. Why not? Seeing the device in action, seeing what it actually does, is very interesting. Why would you deliberately skip that part (unless the device is broken, of course)? It makes no sense.

Sure, it sounds catchy, but it makes no sense.

[tomjones]

Jeez...I stumbled in here to find Dave blowing a voltage standard...now THAT is true electronics porn

[douro]

That resistive opto-isolator says that is assembled in RP...RP is the Republic of the Philippines.

[JamesEncliffe]

I wonder if all the crud on one board came from an earlier failure, where something self-destructed and shot gunk everywhere?

[nonsuch]

In the audio business, we use Vactrols/Opto Couplers a lot. I currently make my own which consists of a CDS cell and an LED facing each other then isolated. I use Black heat shrink tubing. FYI, Yellow LEDs give the best results and choice of CDS will be to your needs.