The tubes last about 15 to 20 years. After that ot's game over.
Agilent sold the atomic clock line to Symmetricom. You can still buy agilent designed systems from them , and they do service them.
I had a gps disciplined clock from agilent. Kinda looked like a 34401 multimeter. Same package.
Came with a huge battery pack and charger. You needed to put a cone antenna on the roof of the building , lightning arresters, and run a big fat coax to the machine. It had a local 10MHz oven that was disciplined by the gps.
58503a with display option. There was a special distribution amplifier that would send the 10MHz out.
I had long bnc coax cables under the raised floor of the lab. If we needed precise timing measurements you would plug thos in the back of the machine and tell the scope/ generator/ counter or logic/spectrum/network analyzer to use the 'external clock'.
You could then do a phase compensation ( due to the long bnc cables ) and have all machinery work in sync. Was used when doing I/Q modulation work on ADSL . The internal oscillators have phase jitter and are outof sync with each other. By linking them up this all went away and we could see how good our electronics was.
I have pictures somewhere of it... Need to look
The little mechanical clock on the front is kinda hilarious. Well, it ticks extremely accurate , but good luck seeing where the hands point.... Measure with a micrometer , mark with chalk , chop with an axe... Bwahaaaahttp://www.symmetricom.com/products/frequency-references/chip-scale-atomic-clock-csac/SA.45s-CSAC/
Herr's the 5071a they talk about. Still in productionhttp://www.symmetricom.com/products/frequency-references/cesium-frequency-standard/5071A/
That company (symmetricom) is really time-nuts. They got it all. Cesium beam standards, rubidium vapor standards, hydrogen masers. You want how many digits ? Come this way ...