Kelvin varley resistor porn - Page 1
Forum section: electronics / testgear

author: ketil b
author_rank: Regular Contributor
timestamp: October 08, 2015, 04:03:29 am
content: HiJust got this of the eBay and thought you guys might like a look at some old-time resistors.There's a bit of an offset error, but nether my meter or my source are calibratedThanksketilEdit : fix the spelling error in the subject

author: ketil b
author_rank: Regular Contributor
timestamp: October 08, 2015, 04:06:41 am
content: And the resistorketil

author: TiN
author_rank: Super Contributor
timestamp: October 08, 2015, 04:20:51 am
content: Sweet, thank you for teardown

author: elex_enthusiast
author_rank: Regular Contributor
timestamp: October 08, 2015, 05:17:50 am
content: Vintage porn beauty!!!..

author: krivx
author_rank: Frequent Contributor
timestamp: October 08, 2015, 07:35:44 am
content: Do you mind if I ask how much? The new prices on Dekapots are pretty shocking

author: ketil b
author_rank: Regular Contributor
timestamp: October 08, 2015, 10:54:53 am
content: Quote from: krivx on October 08, 2015, 07:35:44 amNot at all it was $96 au + $65 shiping.Ya gota get in quick.Ketil

author: Theboel
author_rank: Frequent Contributor
timestamp: October 08, 2015, 11:32:39 am
content: just thinking how to calibrated this beauty ?

author: retrolefty
author_rank: Super Contributor
timestamp: October 08, 2015, 12:31:20 pm
content: Wow those are great pics.What was the retail price and year?

author: ketil b
author_rank: Regular Contributor
timestamp: October 08, 2015, 12:40:39 pm
content: Quote from: Theboel on October 08, 2015, 11:32:39 amThe 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 itKetil

author: AF6LJ
author_rank: Unknown
timestamp: October 08, 2015, 12:44:17 pm
content: Very nice, good workmanship.

author: ketil b
author_rank: Regular Contributor
timestamp: October 08, 2015, 12:51:08 pm
content: Quote from: retrolefty on October 08, 2015, 12:31:20 pmI don't know, there is no dating information on the unit butESI still makes themalthough you will have to get a quote.Ketil

author: PedroDaGr8
author_rank: Super Contributor
timestamp: October 08, 2015, 12:53:06 pm
content: I have FOUR of these badboys. Need to throw a couple of them up for sale sometime soon.

author: Theboel
author_rank: Frequent Contributor
timestamp: October 08, 2015, 01:40:23 pm
content: Quote from: ketil b on October 08, 2015, 12:40:39 pmI think its the best way

author: linux-works
author_rank: Super Contributor
timestamp: October 08, 2015, 01:54:09 pm
content: I bought one of those at my local surplus store (halted, HSC in the bay area):and an old genrad divider that I got on ebay a few years ago:the genrad was $100 or less; but the dekabox was $25 iirc. it was sitting behind a glass display cabinet and after a few visits there, I finally decided to buy this just for the heck of it.

author: K5HJ
author_rank: Regular Contributor
timestamp: October 08, 2015, 02:26:25 pm
content: What happens when you set one of these to divide by zero?Does it blow up?

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 08, 2015, 03:02:29 pm
content: Quote from: K5HJ on October 08, 2015, 02:26:25 pmIt probably would (blow up) if you could set it to divide by zero.CheersAlex

author: Vgkid
author_rank: Super Contributor
timestamp: October 08, 2015, 03:27:28 pm
content: Quote from: K5HJ on October 08, 2015, 02:26:25 pmif you set it to zero, you should get a few microvolts out. Due to reading the voltage developed across the switches. That is in series with the resistors. But it is a guess.

author: linux-works
author_rank: Super Contributor
timestamp: October 08, 2015, 03:30:35 pm
content: Quote from: K5HJ on October 08, 2015, 02:26:25 pmyou get infinite gain. but you get it all at once and it happens way too quickly.

author: linux-works
author_rank: Super Contributor
timestamp: October 08, 2015, 03:33:09 pm
content: Quote from: Alex Nikitin on October 08, 2015, 03:02:29 pmha! genrad gear, from that era, laughs at you. you and I both age, but this stuff never ages. lol

author: AF6LJ
author_rank: Unknown
timestamp: October 08, 2015, 03:33:31 pm
content: Quote from: K5HJ on October 08, 2015, 02:26:25 pmYou Don't Want To Know.They did it to one at Atlantis.

author: Gyro
author_rank: Super Contributor
timestamp: October 08, 2015, 06:16:35 pm
content: Interesting to see how they arranged the staggered wipers on the General Radio Unit.Does anyone know what a non-Kelvin Varley decade divider is called? I have a Muirhead D-801-D four decade "Voltage Dividing Resistance", it is externally the same as a Kelvin Varley divider, ie. It's a potentiometer but uses a different operating principle: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.This arrangement means that there are nearly double the number of resistors (18 matched resistors per decade) and subsequent decades must accurately match the resistance of one resistor on the previous decade (unlike the Kelvin Varley).Does anyone know what this arrangement is called? I would guess that it was built in the '50s so well after the Kelvin Varley divider was invented. Accuracy is very good, still within about 0.02% on ratio as far as I can measure.Here's a link I pulled off the web for general description and external photo. I'll need to open it up if anyone is interested in internal photos.http://rochesteravionicarchives.co.uk/collection/general-purpose/4-decade-voltage-dividing-resistance-box

author: Vgkid
author_rank: Super Contributor
timestamp: October 08, 2015, 06:59:18 pm
content: Varleyvoltage divider. Will update in a few minutes(at lunch).Google is returning it as a plain resistive divider(no fun there).

author: Gyro
author_rank: Super Contributor
timestamp: October 08, 2015, 08:41:43 pm
content: Thanks Vgkid,I suspected (feared) that it would have been invented by either Kelvin or Varley - of course Google completely swamps out with Kelvin Varley references. I've looked in my collection of vintage engineering books but no joy.

author: TimFox
author_rank: Super Contributor
timestamp: October 08, 2015, 11:39:24 pm
content: Quote from: Theboel on October 08, 2015, 01:40:23 pmThe ESI and General Radio Kelvin-Varley dividers use fixed resistors and cannot be calibrated further.The Fluke 720A has trimpots in series with the individual resistors, and a Wheatstone bridge that can be switched to measure each of them separately. It's not necessary that the resistors be precisely 10,000 ohms (for the Fluke), but that they all be equal.If you measure the voltage ratio with a DVM, make sure you are on a voltage scale with very high input impedance. Most DMMs have a finite input impedance for full-scale values above 10 VDC, due to an input voltage divider. The output resistance of the divider is large (66k maximum for the Fluke 720A, which has 100k input resistance), and a 10M load resistance will have a noticeable effect.

author: iampoor
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:57:22 am
content: Quote from: linux-works on October 08, 2015, 01:54:09 pmOff Topic...but how is HSC's surplus selection? Is it priced well?Thanks!

author: ketil b
author_rank: Regular Contributor
timestamp: October 09, 2015, 07:11:09 am
content: Quote from: Gyro on October 08, 2015, 06:16:35 pmI 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?Thanksketil

author: Gyro
author_rank: Super Contributor
timestamp: October 09, 2015, 08:50:02 am
content: QuoteYes, 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.

author: Gyro
author_rank: Super Contributor
timestamp: October 09, 2015, 09:32:40 am
content: 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???

author: ketil b
author_rank: Regular Contributor
timestamp: October 09, 2015, 11:26:33 am
content: They are sume nice swichesI 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.ThanksKetil

author: Gyro
author_rank: Super Contributor
timestamp: October 09, 2015, 11:54:48 am
content: QuoteMuirhead 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.

author: linux-works
author_rank: Super Contributor
timestamp: October 09, 2015, 03:01:39 pm
content: Quote from: iampoor on October 09, 2015, 05:57:22 amusually 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.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: October 09, 2015, 03:46:13 pm
content: Quote from: ketil b on October 08, 2015, 12:40:39 pmThat'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.

author: PA4TIM
author_rank: Super Contributor
timestamp: October 09, 2015, 04:12:27 pm
content: More porn, always nice to see pictures of this grade of instrumentsMy ESI RV722 decaviderMy Fluke 720 insideThe white studs are home made from teflon because the old fall apart.OT but it also has a ESI rotary unitI 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

author: donlisms
author_rank: Frequent Contributor
timestamp: February 22, 2020, 12:01:20 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: February 22, 2020, 12:27:38 pm
content: Quote from: donlisms on February 22, 2020, 12:01:20 pmNo, 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.QuoteAh, 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 iswellwithin 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.

author: GerryR
author_rank: Frequent Contributor
timestamp: February 22, 2020, 03:07:29 pm
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: February 22, 2020, 07:59:21 pm
content: I have 1k ohm ESI DekaPot. One aspect of the porn that is often overlooked is thetactileaspect. Rotating the decade switches feelsjust rightin 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!

author: HighVoltage
author_rank: Super Contributor
timestamp: February 23, 2020, 01:24:14 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: February 23, 2020, 01:48:35 pm
content: You lucky ****I hope they're electrically ok, or salvageable!

author: coromonadalix
author_rank: Super Contributor
timestamp: February 23, 2020, 06:24:13 pm
content: Dang that's beautiful stuff

author: Martin Hodge
author_rank: Unknown
timestamp: February 23, 2020, 09:01:38 pm
content: Reminds me of a Curta calculator. Gorgeous.

author: angrybird
author_rank: Regular Contributor
timestamp: February 24, 2020, 10:37:36 pm
content: 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 meBeautiful resistor, though. Looks tastily inductive