[time-nuts] HP 5065 Meter readings after restoration and adjustments: 2nd Harmonic Problems ?

Ulf Kylenfall ulf_r_k at yahoo.com
Fri Sep 8 03:03:57 EDT 2017

 Having repaired an old 5065 with help from documentson the KO4BB and this list, I took it to my workat Onsala Space Observatory where we have two H-Masers in order to fine tune it.
Initially, the meter readings were close to those listed insidethe protective lid, dated 1987 when the instrument was decomissioned.
Supply = 40Lamp Oven = 24Cell Oven = 28Osc Oven = 48Photo I = 305 MHz = 38Control = 0 (After adjustments)Error = 02nd harmonic 18 (was 30 initially)1MHz/100 kHz = 40
Because it is an early instrument, it did not featurethe thermoelectric device that is recommended forformatting the PhotoCell I used a hair dryer to format itfollowing the advice of Corby Dawson. The 2nd Harmonicvalue was initially at 30, but now it has dropped to 18.
"ON"-time is now ~ 24 hours.
The meter is not stable and the needle is somewhatnervous. When tapping the instrument with a smallscrewdriver, this value jumps up and down.
The instrument is still locked, and after adjusting theSynthesizer & Magnetic field, comparing the 5MHzoutput to that of the H-Maser indicates a phase shiftchange of approx. 0.1 degree in 30 seconds. 
I did the alignment yesterday, and 12 hours later the phaseshift "velocity" has not changed. I also tooka phase noise plot using a Keysight PXA but I do notknow if the plot is a "true" one. There seems to bea pedestal within 10 Hz of the 5 MHz signal after whichthe PN drops significantly. No power line bumpsor other spurii is visible.
My intention is to leave the instrument on for severalweeks in order to see if it is stable. Right nowmy concern is wether the 2nd harmonic readingindicates a wear out of the photo cell.
When repairing the RFV Cavity, all components weretaken out and carefully examined. There wereno dimmed or darkened glass surfaces whatsoever.Apart from repairing the TX heater, the only other thingwas replacing the 1K something resistor in the TXassembly.
Comments invited.
Ulf KylenfallSM6GXV

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