Since at least 2005, a vintage National Company NC-2001 Atomichron has been for sale. This is a first generation cesium beam atomic clock. Although it has a special place in atomic clock history (late 50's, early 60's), the clock was nearly sold for scrap metal due to lack of interest. This is not surprising considering how few people even know or care about this clock or want something this old (50 years), this large (6 feet), and this massive (800 pounds) in their home clock collection. Furthermore, this particular specimen is not in the best condition. I know of two other Atomichron's that look much better. Still, it's a genuine piece of technological and horological history, a snapshot of the state of physics, electronics, and metrology from the 1950's.

Below is the single photo that appeared in the 2013 eBay listing. The photo gives no clue about the condition inside although the description said it was "all there" so that is worth something.

By accident, one evening I happened to be in the city where the clock was stored and was able to take some photos. Time was limited and conditions not ideal for photography, but the pictures below are interesting.

Exterior view

From the front:

From the right side:

Front panel

Front panel, ion current, control signal

Front panel, phase detector

Front view, covers open, by rack, top to bottom

Close-up view of meters

Ion current:

Control signal:

Run-time meter:

Phase detector output and oscillator adjust:

Side view

500/547.18046666 Mc, 100/109.43609333 Mc, 5/5.4718046666 Mc, 20 kc (Zeeman):

Rear view, top to bottom

As a guide to the following photos, here is a diagram from the original NC2001 manual:

Top left wheel on back (or wheel on bottom when entire unit lays flat):

From above, mass spectrometer:

Mass spectrometer, HV connections, view of B-magnet:

Mass spectrometer:


B-magnet, HV connections:

B-magnet, top of cesium tube:

On the left, rear of oscillator adjustment:

On the left, output panel, C-field meter:

On the right, control voltage regulator:

Full view of lower part of cesium tube:

On left, HV power supply:

On right, microwave injection:

Lower end of tube, A-magnet:

A-magnet (note magnetically attached screw and washer):

A-magnet, cesium oven, fallen peeling paint:

Other photos


Favorite samples from the front panel: