CuriousMarc uploaded a video to Youtube showing the startup procedure for an HP 5061A cesium clock [0]. They switch on the clock and compare it to a GPS reference. Seeing the abstract description realized in concrete terms through hot cesium tubes, phase locked loops, and Lissajous curves was really fascinating.

[0] https://www.youtube.com/watch?v=eOti3kKWX-c

Nowadays there's voltnuts in addition to the older timenuts.

The original volt-nuts mailing list pretty much faded away as the members use the eevblog forum now. See the Metrology section.

The time-nuts mailing list is still very active, now in its 23rd year. More info at the group page:

http://leapsecond.com/time-nuts.htm

Quite impressive that a hobbyist got his hands on two working active hydrogen masers. These are still by far the best commercially available frequency standards and cost a few hundred thousand dollar each.

That's the price -- when new. But most "time nuts" buy their atomic clocks well used on eBay or local surplus sales at a massive discount. For example the most recent H-maser on the hobbyist market went for just a few thousand. Granted it was in need of repair, but that journey is part of the fun of an atomic timekeeping at home hobby.