Very interesting. What series resistor did you have these results with? Very interested to compare spec'd temp co. Regards, Chris
Sent from my SMRTphone -------- Original message --------From: Jerry Hancock <[email protected]> Date: 2/20/17 2:51 PM (GMT-06:00) To: kc9ieq <[email protected]> Cc: Discussion of precise voltage measurement <[email protected]> Subject: Re: [volt-nuts] Fluke 332B I took some of the 100K 1/4 watt resistors from my DAS-46 and heated them with a soldering iron. They ran high pretty quickly. I then used a cheap, 1% Chinese brand metal film and they ran high just about as quickly. The 5% Chinese brand ran low a lot faster. Just bringing the soldering iron near them Interesting in that using one of each, the resistance stayed about right on the parallel value. I then used a high quality Vishay and I couldn’t get it to move with the soldering iron without touching it. These resistors cost about .40 per at Mouser. I was just using my Agilent DMM so I’m sure they were moving, just not within the resolution of the meter. The bottom line is that the carbon comp I replaced with the 50 cent per Vishay was a good move. Had I used the 5% I have, it would have been about the same. > On Feb 20, 2017, at 12:36 PM, kc9ieq <[email protected]> wrote: > > Very interesting, very curious to hear your conclusion! > > My thought would be to replace these with standard value 5% resistors having > good temp co, as calibration should surely make up for any subpar values-- > my thinking is that temp drift would be a more major consideration for > overall stability. If this is a false assumption of would certainly like to > learn why. > Perhaps the old Allen Bradley carbon comps were special in this regard, but > the data sheet I've seen for currently available comp resistors had a > horrible temperature coefficient-- much worse than the "better" film > resistors available today. I stock the Vishay PR02 metal films for > rebuilding old tube stuff, which have a temp comp of +/- 250ppm/K. There are > much more stable options out there, but I chose this line because of the 500V > rating and dark red/brown color which blends into an old chassis more so than > tan or bright blue. > > Regards, > Chris > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
