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Originally Posted by powerking
I can only imagine what type of "gear" you are trying to restore here and hopes of some kind of out of this world precision performance you're trying to attain. I would also hope your resistance ranges on your meters for this precision measurement are also calibrated to like 10 to the minus 12 parts per million or something like that (LOL). Why not just buy like qty=10 of DigiKey/Mouser PN PPCHF6.98MCT-ND @ 45 cents each and hand select a near spot on 7.0Meg 6.98Meg(nominal) one? I did this with 10 qty of 1% resistors when restoring the Solar condenser tester and got about 3 of each value nailed on the money (using 2 different DVM's for confirmation); the 7 others in the 10 qty lots were like .5% higher and lower/ in between.
Tom (PK)
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Ok, so that's a vote for the selective breeding style, I had considered but dismissed it earlier, and will probably spend an hour doing some data gathering and analysis with my huge collection of unused resistors tomorrow. I'll model all 3 of my examples, plus I'll grab datasets from any values that I have at least 10 of to model yours. I had earlier presumed that my path would be cheaper than 10x of closest E96 value, but maybe not if I can on average get within 0.2% of target with just running a tournament ladder on 10 cheapies. Also some of the values I may need are truly one-of-a-kind, so those I wouldn't be able to cull by exploiting process variations as easy.
As to my gear and the gear being restored: I try to get 0.5% or better accuracy when choosing contemporary gear for my bench. The things I'm restoring are 5% @ 3/4 deflection nominal accuracy, using 1% parts in places, but mostly 10% or 20%. I'd like to think that with some attention to detail and planning I can achieve 1.25% @ 3/4 deflection.
Think of accuracy as a competitive sport. A batting average of 335 is pretty good, but 350 is still much better.