Tear down of cheap Amazon decade resistor box

[RNA]

So I thought I would check out these cheap decade resistor box from Amazon £16.
I mean how bad could be? 

https://youtu.be/8_Qgr17ZWR0

[TheMG]

Can't say I'm surprised. The switches are the most important aspect of a decade resistor box in order to yield reliable, repeatable results. Good switches of this kind don't come cheap.

Then again, they could have improved that design quite a bit without significantly adding much cost.

[RNA]

What do you reckon about something like these
 https://www.mouser.co.uk/ProductDetail/Grayhill/50P36-01-1-10N?qs=ls7QRyWmRk4Syk7DsxOJAQ%3D%3D
One could make quite a neat compact pcb with six ranges of

100k
10k
1k
100 ohm
10 ohm
1 ohm

[trobbins]

Why would you use Grayhill when imho the Alpha's likely suit the rest of the parts?  I don't recall seeing that you determined the nominal accuracy of the step resistors, or considered a max voltage/dissipation rating to suit their tempco and your application expectations.
https://au.mouser.com/datasheet/2/13/taiwanalpha_12112018_SR2612F-1509903.pdf

[testpoint1]

if you need the accurate calibration tool, you can find a used "General Radio" kit, made in MA USA, but the factory already closed more than 30 years.

[factory]

And hope the previous owner/user hasn't burnt all the precision resistance wire in the lower ranges.
Or it's not rotted away on the higher ranges, from being abandoned in a damp shed/loft/garage for 20+years, as in some Muirhead ones I have.

Having said that I have two nice Cropico boxes, that cover the ranges of the dead Genrad box.
Also have a smaller sized general purpose decade box, of lower spec from Cropico.

David

[RNA]

So over the holiday break my curiosity got the best of me.
I must be clear that my intended use for decade resistor boxes is for the resistors around an opamp to play around with scaling.  Maybe using it to select the brightness of an LED current limiting resistor etc.  Nothing critical.
So I made a prototype by soldering SMD's to a Lorlin switch and was surprised how well it worked.
I decided I would give it a go in kicad and get some made up at PCBWay.com
I will make a video when they arrive and report on how well I did.
Also. I decided not to use banana plugs as there are so many different mounting types and went for soldering breadboard wire for a better connection.

[RNA]

It is so nice when the 3d Models all match up correctly lol

[JimKnopf]

I bought a a similar Mao era style resistor decade a while ago. Too big and not very accurate.
I build this one from thumb wheels. One with old-style metall film resistors, one with SMD parts.

[RNA]

What do you think was the cause of the inaccuracy?

[JimKnopf]

Bad design, bad manufacturing, cheap 5% resistors.

[RNA]

haha that's the same style as in my original video i posted.  I wonder how many of this useless design they have made?  They are all over Shamazon. 

[RNA]

oooh things are coming together now

[RNA]

I am pretty pleased with how this turned out!!  I will make more videos when i can.

https://www.youtube.com/shorts/lhreDVdqf4k?feature=share

[TomKatt]

I am pretty pleased with how this turned out!!  I will make more videos when i can.

Very nice job!

I much prefer rotary switches to the slide switch designs.

Nuts & Volts has a good article about building both resistor and capacitor decade boxes here: https://www.nutsvolts.com/magazine/article/September2016_Capacitor-Resistor-Substitution-Boxes

Often you can find good quality switches at surplus electronic suppliers that are much cheaper than Digikey etc.

[Hamelec]

oooh things are coming together now

Better to use Lorlin CK1059 = shorting type

[RNA]

Yeah. ice idea, and ideally I would like short stubby d-shafts so not have to deal with grub srews.

[Hamelec]

23 years ago..

[TomKatt]

23 years ago..

It goes to 11 

[RNA]

Haha that funny, and potentially confusing lol.  When I designed my decade resistor box I originally had ten resistors.  Limiting to 9 is much easier on the old brain.
One thing that sets my design apart from any lets say non western country is the order of the units.
Mine goes from hight to low as opposed to many others I have seen.

https://youtube.com/shorts/RLTFAFxopnI?feature=share

[RNA]

I made a video using my decade boxes using an example from the MFOS Virtual Opamp.
https://youtu.be/CCaxj9IDMkM

http://musicfromouterspace.com/index.php?CATPARTNO=&PROJARG=ELECTRONICS%2FTECHBENCH%2FTECHBENCH.php&MAINTAB=SYNTHDIY&SONGID=NONE&VPW=1314&VPH=827

[TomKatt]

That virtual op-amp page is pretty slick!