Electrical Metrology- "Converting a Leeds&Northrup Ayrton Shunt Box to a 0.03% R

[GEOelectronics]

link to:  "Converting a Leeds&Northrup Ayrton Shunt Box to a 0.03% Resistance Standard"

 http://www.qsl.net/k/k0ff/VOLT_NUTS/Ayrton_Shunt_Conversion/Leeds-Ayrton_Pub_25.May.2018.pdf


Geo>K0FF

[Gyro]

Nice easy conversion and writeup. 

A couple of suggestions:

- With minimal wiring mods (cutting the link between the wipers on the two wafers and moving one wire), you could convert it into a 4 wire kelvin sensed resistance standard with sense on the other terminals. It would eliminate variations due to switch contact resistance. Probably most useful on the three lowest values.

- The Metal disc on the knob is almost certainly attached with screws. You could turn it upside down and add more permanent markings.

Both mods would be easily reversible.

[GEOelectronics]

Good points, thanks Gyro. Yes the dial is held in place by screws. There are two different versions of the dial, both are easily hackable. Soon I'll post my 4 wire resistor standards build, made with 5 and 10 Dollar eBay finds. (mil spec Vishay metal foil resistors).

Not volt-Nuts standard but way better than anything I had before.
Geo>K0FF

[Vgkid]

Look into my 4385 teardown to see how they implemented a 4-wire setup.
https://www.eevblog.com/forum/metrology/ln-4385-teardown/

[GEOelectronics]

Thanks for the link and teardown L&N. Yours looks like mine. There are a number of "Boxes" from (evidently) different vintages that use same circuitry and box, but much different style knobs. The newer (I assume) ones are black and have a shroud over them.
Personally I like the metal disc look.

The attached picture I caption" You might be a Volt-Nut if this is your idea of an adjustable resistor!"

Notice the file marks on the flattened section of one wire?

We used to "trim" carbon resistors with a file. I write that up sometime.

Geo>K0FF

[Vgkid]

You wouldn't happen to have a 7593 would you. That was the most expensive L&N "box".

[GEOelectronics]

Had to go write down a short inventory. Here's what I'm working with at the moment:

VOLT BOXes:
1 X 7592 with Black Plastic (Bakelite?) Knob shroud and black dial skirt
1X 7592 with silver knob skirt.
 
2 X 7593 with all clear terminal insulators and silver color metal knob skirt
1 X 7593  with clear and colored (red+black) and silver knob skirt

SHUNT BOXes:
1X 2664 Ayrton variant High Resistance Silver knob skirt
1X 4385 Low Resistance Black knob shroud and skirt
0X 4385S can't find this one, maybe didn't win it?

Are you a collector? Have data posted on any Volt Box?

May I use your schematic drawing of the 4385 (with credit given) in my eHam article? If granted ow shall I credit?

I like this sub board much better.

Geo>K0FF

[Vgkid]

You can  post my stuff.
 This was originally posted to the volt nuts list a few years ago , then TiN hosted it on his site.
https://doc.xdevs.com/doc/L%26N/LN1972.pdf