09-10-2019, 10:45 AM
(09-10-2019, 10:07 AM)Amie Wrote: Dad told me that when he was first interested in electronics and was building something that required say 2% components, he would (in ignorance) try to select values from a batch wider tolerance types, apart from other problems, he found that the values of 20% resistors for instance would be within 20% but outside 10%, he says probably because they were selected from production runs as 5%, 10%, 20%.
Your dad was almost certainly correct. Back then the usual way was to sort, then mark. So selecting the 5% parts ensured that the 10% parts were rarely closer than 5% etc.
Modern manufacture is sufficiently accurate that this really doesn't happen with resistors. Not so sure about some chips. For example programmable logic chips are often available in different speed grades. It's likely (though I have no real evidence) that the makers test all the devices and select the faster ones. Hence if you buy a slower grade it really will be slower. Though sometimes all the parts will be fast enough for the faster grades and they will deliberately mark them as slower. Why? If there aren't enough customers for the fast parts, the higher price, they can still sell them cheaper rather than alienate customers.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv