Display and counting tubes
tubes Filament indicators Neon 7-segment
These neon-filled numeric displays, also known as 'numicators',
consist of an outer mesh anode, with ten cathodes (or 11/12 with decimal point/points)
shaped to form numbers. They were popular in the 1960s and early 70s when the first logic
ICs became available, the 7441 or 74141 TTL devices often being used as a driver, and can
still sometimes be seen in old electronic test equipment. I can provide custom-built nixie displays for TV/Film use - please email if interested.
Left to right : Standard tube (probably Mullard ZM1175), Mullard ZM1080,
with orange coating on glass to improve colour, Unusual ITT tube with sine, spiral, minus
and plus indicators, 'stretch NE-2' lamp used as first digit in 3½ digit display,
Valvo/Ultron ZM1042 1.3" high digit.
Huge 6" nixie Type CD47/GR414 RODAN Indicator Tube by Okaya Japan,
plus East German 2" and 1.3" tubes (picture from Jorgen Lund-Nielsen),
Burroughs B7971 2.5" alphanumeric tube, Okaya CD13 0.3" subminiature tube - as
used in my nixie car clock.
Three end-viewed nixies, 1" STC GN-4D, 1.3" Cintel 'Cathvisor'
N.I.7, 1.5" STC GN-5 (sizes are bulb diameter).
Giant National NL-8091 tube, digit height 1.5", tube dia. 2"
A 'pixie' tube, which lights a neon glow on one of ten plates behind a
numeric aperture mask. Unlike nixies, this one seems to have a common cathode and
ten anode connections - sounds odd but this is the only way I could get this tube to
display properly. Markings worn off - probably made by Valvo. Info
on Burroughs Pixie tube.
Dekatron counter tubes
These 1950's tubes function both as counters and displays. The one below left
(Ericsson GC10B) has 30 cathodes arranged around a central anode disc. Each cathode is
connected to one of three external pins, forming ten electrode groups. Applying three
sequentially phased pulses to these pins makes the glow discharge jump from one electrode
to the next. An external phase-shift network is used to provide the sequencing, resulting
in a counter that advances the glow by three electrodes for every single input pulse.
These tubes were often used in geiger and frequency counter applications, and as
prescalers for a mechanical counter, count rates of 20-100Khz being possible. Other
variations included divide-by 12 tubes, tubes with seperate connections to all ten cathode
groups (to enable divide-by-N operation - second photo), and display-only versions
with ten electrodes, which were used to provide a consistent-looking display on
instruments using a combination of high-speed valve dividers and dekatrons. Note that in
the photo below, the exposure time makes more than one electrode appear lit. Got some
dekatrons? Here are a couple of simple circuits to bring them to
Ericsson GC10B & GS10C, Hivac GS10H, 17 pin base, 1.5" high.
Detailed description of dekatron operation
from 1954 Ericsson data book, including datasheets. Info on an early dekatron based
computer Data sheets for Elesta (Swiss) EZ10/10B
dekatrons Original advertisment for dekatrons
Another related device was the Nomotron (G10/240E),
which was a unidirectional counting tube, made by STC from 1951. It used only a
single-phase input, as opposed to the three of the dekatron. The discharge was directed
between the ten cathodes by means of special electrode shaping, and the tube was capable
of counting at up to 25KHz. The count state is visible through small holes in the front
electrode, but as th eglow is small and rather hard to see, this was really only useful as
a diagniostic aid rather than a proper display. See this old
advert (Electronic Engineering, July 1951).
The tube contains ten main cathodes (k0 to k9) brought out separately
to base pins. The cathodes are equally spaced around a circle and between each is a
transfer electrode (t). The transfer electrodes are joined and taken to a single base pin.
Around the cathodes is a single anode cup and there is a shield to restrict the glow to
If a glow discharge be assumed between the anode and ko, the potential between them will
be the normal maintaining voltage of a gas-filled valve ; the difference between this and
the anode supply voltage is the voltage drop across anode and cathode load resistors. The
asymmetric geometry of the cathode and transfer electrodes makes any shift of the glow
discharge inherently unidirectional. When a negative pulse is applied to the transfer
electrodes, the discharge is compelled to spread to the most strongly primed transfer
electrode tt and the fall of anode voltage (due to increased current in the anode
resistor) extinguishes the anode k;, gap. At the end of the negative pulse, tt will return
to its positive bias potential and since k,~ is positively biased by the residual charge
in a capacitor in the cathode circuit the discharge moves to the most strongly primed
unbiased electrode, i.e. k1. At first, the discharge transfers to the cathode
"tail" but quickly moves to the main part of the cathode to avoid the excessive
maintaining voltage associated with high current concentration on the small tail area.
Priming of tz is thus effected in readiness for the next transfer pulse.
<Burroughs 'Beam-X switch' type BX-2004
Another type of counting device, a crossed-field decimal counting tube - more info on
these devices Here.
This was purely a computing tube, and didn't display, but could drive a nixie tube. It originally had a metal magnetic
shielding sleeve covering the tube, which has been removed on this example. The base has
26 pins. Mullard also produced a similar device, the ET51 Datasheet
here Original press report on Burroughs tube Datasheet for ETL
> Valvo (Later Mullard) E1T, an electron-beam
count & display device, using a fluorescent screen to display the count. Datasheet here.
Neon 7-segment displays
These were the immediate ancestors of modern LED 7-segment displays, and
are still used for some large-display applications.
Sperry SP-151 display from Heathkit car clock (half inch digits) Data, Tung-Sol Digivac S/G DT-1704B,
modern Japanese (make unknown) NEO-8000M flat-panel display (3.5" digit)
Before LEDs, filament lamps were also used for digital displays. To my
knowledge there were three basic types of these:
1) Segment displays which used linear filaments as
segments, the whole display being encapsulated in a sealed glass enclosure. These were
made in in both rectangular Dual-In-Line and nixie-style 'bulb' packages , the former in 1
and 2 digit versions. Sometimes known as 'minitrons', these can occasionally still
be seen in old petrol pumps.
Images : Japanese 7-segment DIL packaged display, 'Pinlites' 14-segment alphanumeric
display, RCA DR2000 'Numitron'
2) Projection displays, using
ten lamps with a digit mask in front of each, and optics to project the digit onto a
translucent screen at the front. The only place I have ever seen these is in an old
digital voltmeter. Thanks to Richard Schipper for the picture (right) of a display made by
Counting Instruments Ltd, Borehamwood, Herts UK. On the left is a russian projection
display, picture from Alexander Bakerin.
Tiny projection displays
"IN-LINE Digital Display Type 70" by Counting Instruments, UK. These plug into a
mounting frame to allow easy access for lamp changing Digit height is 9mm, module size is
20 x 12 x 47mm. The digit masks are made from a piece of photographic film, and 3 sheets
of moulded plastic lenses provide the required optics.
The Counting Instruments company appear to have
also ventured into areas other than digital displays - These fairly large ones look like
they were destined for fruit machines (Slot machines / one-armed bandits). Thanks to Pete
Crunden for the following info : The fruit-machine display was probably used in a
machine. I remember seeing something similar about 10 years ago while on holiday in Spain.
I learnt later (while working for Barcrest) that the Spanish government (in a somewhat
lame attempt to make things harder for fruit machine manufacturers/operators, without
actually banning slot machines altogether) used to have a law whereby the reels of a fruit
machine could not be greater than 1½" in diameter. They got round this by using
projection displays (like yours) or two small (legal)reels, between which was threaded a
sort of conveyor belt on which were printed the fruit symbols. These 'flat' reels were
rather clumsy devices (noisy and heavy on current), but are still used occasionally for
Another variant on the projector theme was the meter movement based display used in
this old Venner frequency counter
3) Side-lit light-guide displays. These used
sheets of thin glass, each having an engraved pattern of 'dimples' which lit up when light
was shone into the edge of the glass sheet. I recently picked up a box of these (KGM
Multi-Indicator Type M25), pictured right, and built a clock
with 4 of them based on my Nixie Clock design. The body is
an aluminium block, which houses the lamps and acts as a heatsink.