Walter, did you check on both failing oscillators, that the ovens work properly afterwards, or that the cases still get warm? I once had a failing 10811, where the NTC was defect, maybe also after a longer unused time. As the heater draw an excessive current on turning on, (about 500mA for the 10811), maybe the thermal fuse blew up, but due to the peaking current, not due to temperature. I find it quite unusal, that the oscillator / XTAL itself should make a jump like this. After 48h at most, it should return to its recent frequency trimming, within < 1E-8, or less.. as these guys are really old. That's the typical behavior of all three 10811, which I own (inside 5370B, 5335A, and one external). Frank

Hi A failed ( = cold) oven on either a normal OCXO should give you a “tens of ppm” sort of frequency error. At 10 MHz that would be over 100 Hz. Fractions of a ppm are less likely to be oven issues. Bob > On Nov 5, 2018, at 1:01 PM, Dr. Frank <frank.stellmach@freenet.de> wrote: > > Walter, > > did you check on both failing oscillators, that the ovens work properly afterwards, or that the cases still get warm? > > I once had a failing 10811, where the NTC was defect, maybe also after a longer unused time. > > As the heater draw an excessive current on turning on, (about 500mA for the 10811), maybe the thermal fuse blew up, but due to the peaking current, not due to temperature. > > I find it quite unusal, that the oscillator / XTAL itself should make a jump like this. > After 48h at most, it should return to its recent frequency trimming, within < 1E-8, or less.. as these guys are really old. > > That's the typical behavior of all three 10811, which I own (inside 5370B, 5335A, and one external). > > Frank > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.