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 six New Old Stock
Ultronics branded B-7971 tubes with original Burroughs Data Sheet as spares that I
purchased back in the early 1980’s for around $5 each (versus $4 for used tubes
pulled from Lectrascan cards – the extra $1 seemed
worth it for new tubes), one used Burroughs branded B-7971, 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. PLEASE NOTE: From time
to time I receive requests to purchase my spare tubes. They are spares and they are not for sale.
With B-7971 prices now USD$200 and higher each for used tubes, when they are even
available for sale, having to replace them at a future date would be cost
prohibitive and they cost me nothing to store.
If at some future date I do decide to sell them, I will put them on eBay
but I suspect that will be up to my heirs to decide.
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.
Last modified January 14, 2022