Kelvin varley resistor porn

[iampoor]

I bought one of those at my local surplus store (halted, HSC in the bay area):

Off Topic...but how is HSC's surplus selection? Is it priced well?

Thanks!

[ketil b]

Instead of each decade bridging two resistors on the previous one, on the Muirhead each decade replaces one resistor on the previous one... It actually has roughly twice the number of resistors per decade (apart from the last one). Each switch has 2 wipers, one selects from a chain of up to 9 resistors below the tap and the other selects from a chain of up to 9 resistors above. Eg, when set to 5 it selects 5 resistors below and 4 resistors above - the next decade replacing the 'missing' resistor.

I have been trying to visualize this all day and I have to say I've been failing.

So there are two strings of 9 resistors in each decade, are they in parallel or is one end of each string floating?

Thanks

ketil

[Gyro]

So there are two strings of 9 resistors in each decade, are they in parallel or is one end of each string floating?

Yes, that's correct, 2 strings of nine 1k resistors (one end floating) in the first decade, with the second decade having a total resistance of 1k (assuming the next decade is also present...and the following one). If you opened the connections between two decades then you would get open circuit. The final decade is just 10 resistors with a single wiper, straight potentiometer (as with a KVD)

It does seem a huge overkill over Kelvin Varley - very good for showing off your resistor construction and matching capabilities  . I can't work out if the extra complexity adds any benefit over KVD. I suppose it makes the switches (big stud ones like the General Radio) a little simpler - They still have two wipers but they are on opposite sides (one for each resistor chain) rather than having to be staggered two studs apart on the same chain, but that isn't sufficient reason.

EDIT: Actually I lie (haven't had it apart for a while). The Final decade is also two chains of 9 resistors, with the two wipers connected together as the tap. Now that's taking things to extremes!  I'll post photos.

[Gyro]

Ok, here's my non-KVD Divider resistor Porn!

Switch contacts are Silver or Silver plated.

Edit: Actually looking closer again, there are 20 resistors per decade (2 chains of 10) but the first three decades only use 9 positions so 2 wasted resistors. Clearly built as 'standard blocks'... The economies of mass production???   

[ketil b]

They are sume nice swiches

I also can't see the advantage over a KVD, but then if there making standard 10 resistors blocks then it might make sume sense.

What the input and output impedance of this, the resistors in the last decade look quite small.

Thanks

Ketil

[Gyro]

I also can't see the advantage over a KVD, but then if there making standard 10 resistors blocks then it might make sume sense.

What the input and output impedance of this, the resistors in the last decade look quite small.

Muirhead made all sorts of instrumentation so they must have had some reason, searching on the web, they did also make a KVD so there must be some difference.

It's a 10k input resistance divider, so the highest the output resistance would get to would be 6k666 for a low resistance source, normally much lower. The Resistors are 1k in the 1st decade, 100R in the 2nd, 10R in the 3rd and 1R in the last. Residual output on the Divide by Zero 'end of the world' setting is a stable 11uV @ 10V input, so 1ppm.

I keep meaning to build a decent buffer for it so that I can use it as a precision power supply. It's not a problem for normal DVM input resistances.

[linux-works]

I bought one of those at my local surplus store (halted, HSC in the bay area):

Off Topic...but how is HSC's surplus selection? Is it priced well?

Thanks!

usually good and fair prices.  their test gear is hit and miss; some stuff is very overpriced and sits for years, there, on shelves.  small parts are usually a great deal, though.

[MLXXXp]

just thinking how to calibrated this beauty ?

The quick answer is you don't, or there is nothing inside that can be altered.

The best you can do (and I suspect that this is how it was done back in the day), is you get a very good voltage reference and a very good DMM and make a list of the error for each dial setting. Then apply that error every time you use it

That's what was done with the little Cornell-Dubilier boxes that I have. Sorry, they're not as "pornographic" as the ones others have shown.

[PA4TIM]

More porn, always nice to see pictures of this grade of instruments

My ESI RV722 decavider


My Fluke 720 inside
The white studs are home made from teflon because the old fall apart.


OT but it also has a ESI rotary unit

I have no information about this ESI LCR bridge other then that is was made in the 60's and part of a set (with a generator and detector)
The inside:


Besides that I have ESI resistance standards and some resistor decade boxes from Siemens, General Radio and Danbridge. The Siemens inside pictures are not suited for publication, they are hardcore porn

[donlisms]

Digging up the past -- isn't the thing to do?

I just acquired two more nice old Dekapots, and stumbled across this thread while poking around.  The "non-Kelvin-Varley" divider intrigued me.  A related web page has this comment: "The instrument can also be used as a decade resistance box."  I think that's the answer -- tha advantage over K-V.  All you'd have to do is disconnect the upper resistor chain.

I'm not sure you could do it with a K-V; I haven't tried to work it out, but on the surface, I'm guessing it would be rather difficult, mechanically speaking.

[Gyro]

Digging up the past -- isn't the thing to do?

No, It's a good thing to do when it is a thread full of pretty pictures... and maybe a chance of encouraging a few more.

I just acquired two more nice old Dekapots, and stumbled across this thread while poking around.  The "non-Kelvin-Varley" divider intrigued me.  A related web page has this comment: "The instrument can also be used as a decade resistance box."  I think that's the answer -- tha advantage over K-V.  All you'd have to do is disconnect the upper resistor chain.

I'm not sure you could do it with a K-V; I haven't tried to work it out, but on the surface, I'm guessing it would be rather difficult, mechanically speaking.

Ah, I think that was mine (the Muirhead Voltage Dividing Resistance). Through the kindness of a fellow member, I now have the datasheet (attached), in which they describe it as Rayleigh type divider. [EDIT: which I think is basically just a true potentiometer].

Yes being able to use it as a decade resistance box is useful, unfortunately that also opens it up to the sort of accidental overload abuse that resistance boxes eventually seem to suffer. Luckily mine seems to have escaped and is well within spec on all settings. Muirehead did also do a KVD, which had an extra decade and another leading zero on the accuracy spec. I'm still trying to get my hands on one at reasonable price.

[GerryR]

I bought a K-V divider sometime ago, but when I received it, it was damaged due to poor packaging.  I got it at such a good price that I decided to keep it and repair it; there was only mechanical damage, electrically it was perfect.  I then boxed it up to make it a little more usable.  This is a 10K version.

[tggzzz]

I have 1k ohm ESI DekaPot. One aspect of the porn that is often overlooked is the tactile aspect. Rotating the decade switches feels just right in a way that can only be experienced with fingertips.

I also have a 100k ohm 7decade Julie Labs KVD, a Real Man's Tool. It is a delight to use since it has a switch that connects the outputs to the KVD output (obviously) but also the KVD input and ground.

But inside it is much more boring: just a few sealed boxes that you really don't want to open since they are oilfilled. And that makes the KVD damned heavy!

[HighVoltage]

I just got lucky, buying one Kelvin Varley divider for cheap and the seller asked me if I want 4 more for free.
They look like they have been abused and I will have to take them apart and see, if they can be revived.
So, may be soon, I will add some pictures of the inside to this thread.

[Gyro]

You lucky **** 

I hope they're electrically ok, or salvageable!

[coromonadalix]

Dang  that's beautiful  stuff

[Martin Hodge]

Reminds me of a Curta calculator. Gorgeous.

[angrybird]

You guys responded to this old thread, I saw reference to HSC, GOT ALL EXCITED LIKE MAYBE IT HAD OPENED AGAIN and then saw the date.

Why do you do this to me

Beautiful resistor, though.  Looks tastily inductive