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GrimJosef · 17th May 2018, 9:10 am

Ah, OK. I was working on E12 values for the fixed resistors but I knew that the pot would almost certainly be 500k, not 470k because, well, they just are. (It couldn't be much less than 500k because you wouldn't be able to measure 443k across it if it was. And it couldn't be the next value up - 1M - because R8+R9 has to be at least 1M7 and that's not low enough to deliver 443k when it's in parallel with 1M.)

Once I'd got the pot value I needed a few megs in parallel to get 443k. I found I had to raise the pot value a bit to get the other two results to converge on your measurements (one from below and one from above).

Now you come to mention it I had heard of the delta-star equivalence. But there's no way I'd have remembered it if I'd needed it in anger, so to speak.

Cheers,

GJ

17th May 2018, 9:10 am	#8
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Resistor puzzle Ah, OK. I was working on E12 values for the fixed resistors but I knew that the pot would almost certainly be 500k, not 470k because, well, they just are. (It couldn't be much less than 500k because you wouldn't be able to measure 443k across it if it was. And it couldn't be the next value up - 1M - because R8+R9 has to be at least 1M7 and that's not low enough to deliver 443k when it's in parallel with 1M.) Once I'd got the pot value I needed a few megs in parallel to get 443k. I found I had to raise the pot value a bit to get the other two results to converge on your measurements (one from below and one from above). Now you come to mention it I had heard of the delta-star equivalence. But there's no way I'd have remembered it if I'd needed it in anger, so to speak. Cheers, GJ __________________ http://www.ampregen.com