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Numitron Clock Project

Posted on February 21st, by Shaun Merrigan in Tech, Time and Frequency, Vacuum Tubes. Comments Off on Numitron Clock Project

Numitron Clock Project

Numitrons are low voltage incandescent display devices perfected and marketed by RCA (see RCA advert above) in the early 1970’s.  I would call this a bridge technology as the display is incandescent, but can be driven by integrated circuits.   They were quickly displaced by solid state LED (light emitting diode) devices from the mid 1970’s onward.

This is a Numitron:

RCA Numitron Advert

RCA Numitron Advert

The look and feel of a Numitron display appeals to me and I wanted to reboot my building and soldering skills , so I decided to build a Numitron clock.  I based my clock on the RCA DR2000 which has a beautiful 15mm display height and a board and parts kit (no longer available) from Richard White.  Here are some images of the construction process:

Assembly Process (1)Assembly Process (2) Assembly Process (3)   Assembly Process (5)Assembly Process (4)

And here is an image series of the finished clock just before, at, and just after 0000, January 1, 2015:


Numitron New Year 2014 059Numitron New Year 2015 000Numitron New Year 2015 001


Here is a video of the clock counting to New Years Day 2015

Next I have to decide on case design and construction.

From a Time and Frequency metrology perspective, it is fascinating to watch how the clock corrects on a daily basis.  It is locked to my local 60Hz AC line frequency, which means it can be as much as +-8 seconds at at any given second.  However during a 24 hr period, it will be corrected and never accumulates any more error than +- 8 seconds.  It has been running for six weeks continuously as of this writing and it is about +3 seconds (vs my  GPS locked UTC clock).  However earlier today it was less than 1/2 second ahead.

More to follow…..

(Yes, the clock worked the first time I powered it up)

Shaun M

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