Ring vs BCD counters for decades

Rick Bensene rickb at bensene.com
Sat Aug 30 13:06:04 CDT 2008

The first electronic calculator, the Anita Mk 7, used 10-stage
thyraton-based ring counters.  The machine was essentially an electronic
implementation of an electromechanical calculator.  The ring counters
were of a very unusual design, developed by Norbert Kitz, who was a
master of thyratron circuitry, and also a major proponent of pure
1-of-10 (decimal) representation for use in electronic calculating
machines.  He said at one point in a paper referring to his design ideas
something to the effect (can't remember the exact quote at this moment)
at "no silly binary is needed here".

The ring counters connected directly to the Nixie tube for the display.
The Nixie tube was an active part of the counter advancing circuitry,
such that the digits were "stacked" in the Nixie in a special order to
allow the firing and shutdown of the nixie digits to stabilize the ring
counter such that it would step very reliably one count at a time (even
at relatively high clocking rates for thyratron circuity), as thyratrons
were a bit picky as far as circuit parametrics went.  The design was
quite brilliant, and very efficient, as absolutely no decoding was
needed at all...the 10-thyraton ring counter and the Nixie tube worked
together synergistically.  The Nixie tubes were custom-designed for this
circuitry.  If someone has one of these old machines (Anita Mk7, Mk8,
and Mk9), and a Nixie is bad, an exact replacement has to be found, as
not just any Nixie tube will work.

The Mk7 calculator was made in very limited production, as it had some
stability issues, which were refined in the Mk8 (and the overall
circuitry simplified a bit).  The Mk8 was quite widely marketed, and

I have an exhibit on the Mark 8 on my Old Calculator Museum website (a
schematic of a digit stage is included there) at

While thyratrons are much different than vacuum tubes, the Sumlock/Anita
calculators based on this technology were quite amazing for their time
(introduced in 1961), and on their own, created an entire new
market...the electronic calculator.

Rick Bensene
The Old Calculator Web Museum

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