Burrough's B-7971 Nixie Tube Clock
Front
Back
These are front and back pictures of a Burrough's B-7971 Nixie Tube clock that I built back in
1979 when I was a senior in High School. The digits are 2½ inches high which
allowed me to read the clock from anywhere in my bedroom without needing to
wear my glasses. The clock circuit is based on a schematic (page 1,
page
2 and page 3) that had been provided by the surplus parts vendor
along with three Ultronic Lectrascan
display cards which were part of an Ultronic
Systems Lectrascan. The six B-7971 tubes and SK137 sockets (NSN 5935-00-847-8641) used
with the clock came from the Lectrascan cards. The Lectrascan cards also had high voltage switching
transistors (2N1302 and SA480) that were used in the construction of the clock.
The clock uses a National Semiconductor MM5311 clock chip for time keeping and
uses the 60Hz line frequency as its time base which is reasonably accurate.
Unfortunately, the original circuit was a very poor transformerless
design and blew several capacitors, resistors and Zener
diodes during its initial test run (it was a spectacular explosion!). I wound
up making my own design changes, including adding a transformer, and it has
worked fine ever since it officially went "live" on February 11,
1980. Over the years, I have replaced
some parts with newer smaller components but it still uses the original clock
chip and high voltage transistors that came from the Lectrascan
cards. Back in 1979, I was a cash
strapped student and did not have the money to purchase the best parts except
for a rather hard to find 160V/10W Zener diode, used
for regulating the high voltage, that I obtained surplus for a very low price. I designed the PC board and wooden stand
myself.
I currently have seven brand new spare
B-7971 tubes that I purchased back in the early 1980’s as well as five spare
MM5311 clock chips and one complete Lectrascan card still equipped with its SK137 sockets. However, after almost 30 years of continuous
operation (the clock took a break when I was away at college), the original
tubes are still working fine and show no signs of needing replacement so the
spare parts remain in storage.
To learn more about Nixie tube clocks,
visit Mike
Harrison's Nixie Tube Clock Page at http://www.electricstuff.co.uk/nixclock.html.
Be sure to visit the Nixie Clock Gallery at http://www.electricstuff.co.uk/nixiegallery.html
where this clock is also listed.
The IEEE published an article on Nixie Tubes in their June 2002
issue of Spectrum.
The article is available at http://spectrum.ieee.org/consumer-electronics/gadgets/new-life-for-nixies.
It is also available at http://www.amug.org/~jthomas/ieeenix.html.
Last modified September 27, 2010