Hi Most potentiometers have very good TC when used in a “ratio mode”. You can quickly mess that up by putting resistance in series with the pot. It’s a bit surprising how may times you see this inherent stability messed up that way.
Bob > On Aug 29, 2015, at 9:03 AM, Adrian <rfn...@arcor.de> wrote: > > Keep in mind that potentiometer R6 is one of the key components of the > C-field circuit. > Together with R8 and R12, it defines the reference voltage to Q6A/B. > The tempco of that wire-wound potentiometer can certainly not be neglected. > > I would suggest to check the C-field temperature dependency with an > external precision current source feeding the C-coil directly. > > Adrian > > Poul-Henning Kamp schrieb: >> Using the Fluke 732A as voltage reference improved HP5065A stability, >> but not very much, so I looked closer at the constant-current >> generator and the C-field pots "calibration": >> >> http://phk.freebsd.dk/hacks/HP5065A/20150828_c_pot/index.html >> >> ... and found out that the current-sensing resistors R10||R11 have >> a very high temp-co. >> >> Getting closer... >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.