Chinese decade resistance box teardown photos

[iloveelectronics]

Having watched Dave's recent teardown video of his auction scored metrology grade decade resistance box, I thought it might be a good idea to get one of these boxes. I don't have thousands of dollars to spend on one so I look north of border to China 

This thing claims 0.1% accuracy on most of the ranges and does seem to be within spec according to my second hand HP3457A (which I have no idea when it was last calibrated). It actually isn't exactly very cheap by Chinese standard, costing me over $150, but for a 8-decade box I thought it wasn't too bad. If nothing else it'd at least be slightly interesting to see what it is like inside

[retiredcaps]

Thanks for sharing the photos.

At this point, I can't see myself needing a decade resistance box.

[SeanB]

Interesting in how they only use 6 resistors per decade. Looks very nice inside.

[Paul Collins M0BSW]

I'd be interested in one, I used my 5% home made one,to great use when I got a radio in where the resister had gone high and stopped it working, with no viable  colours showing,just heat marks so I hooked up the box, set it high and kept lowering until it jumped into life, measured the resistance, put the closest value in ,job done , this may not be the formal way of doing things , but it worked for me.

[iloveelectronics]

One thing to note about this decade box is that it actually says “DC resistance box” in Chinese on the front panel, so apparently it is not designed for AC circuits. It has rather significant inductance due to all those coils.

I am ordering an AC one (but only 6 decades 0.1-111k ohms) for a customer. Will be getting an extra one too just so I can have a look myself

[MJLorton]

I missed this...

Thanks for the post Franky...I like it!

Decade boxes are not cheap so if the 3457A is happy with it...it looks like a great buy, even if only for DC.

[jadew]

Nice!

I've been looking into buying one myself, but I can't get myself to spend all that money on it. Building one might be cheapper, however, I had a hard time finding cheap 9/10 position switches.

If anyone knows where to find these sort of switches on the cheap, I'd very much like to know.

[SeanB]

Yopu have a choice with the switches. Cheap and nasty ( in that case 5% resistors are usable to do an E12 decade box) or quality and a little more expensive, which are usable with 1% resistors.

[tmm]

Using 6 resistors per decade is quite clever - i assume each resistor is twice the increment value and they parallel two of the resistors for all the odd positions.