[time-nuts] hp 10544A and 10811A ovenized oscillators

[Dr. Frank]

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