(Click on either Figure for a larger version.)

Gas-Discharge Display More commonly referred to as Nixie, the gas-discharge tube was introduced by the Burroughs Corporation in 1955. It is basically a cold-cathode tube (Figure 9-14) with separate cathodes in the shape of characters. When a sufficient potential is applied (approximately 175 volts) between the selected cathode and plate, the gas surrounding the selected cathode is ionized and glows. Other types of gas-discharge displays are available having glow-bar segments to form in-plane characters and also cathode rods to illuminate a printed or cut-out character.

Figure 9-15 shows how a typical gas-charge display tube is driven from TTL logic. IC-7490 is a decade counter with parallel BCD output and serial count input. The overflow from the counter is used to operate the next more signficant digit display. The BCD counter output is fed to a quad bistable latch (IC-7475) which acts as a memory storage. The count is stored in the IC until a strobe pulse allows the output of each latch to change. This prevents the display from being a blur of changing numbers. The BCD output of the latch is decoded by IC-7441 (BCD-to-decimal decoder/driver) to a one-of-ten decimal output. The IC also has high-voltage driver transistors to drive the cathodes of the tube.

Where character readout is required multi-cathode gas discharge tubes are used. One method of construction is to make each cathode the shape of the character to be displayed. For example one tube might have 10 cathodes in the shape of numerals 0 to 9. To cause the required cathode to glow a suitable voltage is applied between the anode and the selected cathode.

Typically the discharge will strike at about 80V and burn at about 60V. The circuits to drive such tubes must therefore be able to supply such voltages.

A suitable circuit is shown in Fig. 16.9. Note that when Tr₁ is off the collector does not rise to +150V but is 'caught' at about +80V provided one of the other cathodes is energized.

The disadvantages of this type of indicator are:

1. The characters do not lie in the same plane.
2. The number of characters in one tube is limited to about 12.

The advantages of this type of indicator are:

1. The characters are well-shaped.
2. The characters are bright and can be large. (Tubes with characters up to 3 in high are available.)

• 7441 - Early BCD Nixie driver

This part was also sold by Radio Shack as catalog number 276-1804.

• 74141 - BCD Nixie driver
• 8T - Signetics Nixie Driver: Click here for the datasheet.

Click here to view an index to several construction projects from the magazine Radio-Electronics.

You can read the note by clicking here.

From the data sheet:

The Radio Shack #276-048 is a cold cathode, side viewing numerical indicator tube. It displays the numerals 0 through 9 and has two internal, independently operable decimal points located to the left and right of the numeral. The desired numeral is lit when its corresponding cathode is energized. The color of the display is neon red. The brightness of the numerical indicator is dependent upon cathode current, and the horizontal viewing angle is 100 degrees.

Click here to see a scan of the datasheet.

One of the smallest Nixie tubes is the Burroughs B4998, a top-view design

I have a display module from an old piece of test equipment that has six of these display tubes.

From Stuart Walker:

I can tell you that the driver chip is a Fairchild 996079 sometimes called a 9960 or 960, shortly after 1969 they became obsolete and were part of a family of chips called CUL or Counter micrologic. They were peculiar in that they took an inverse binary input and therefore needed the matching transistor or IC, therefore the transistor is possibly a 995879 sometimes called a 9958 or a 958, which was a decade counter and either available in the 8 pin transistor package (to 5) or 14 pin dual in line package.

You can see more photos and information by clicking here.

They have a very interesting decoder design using neon lamps (hidden under the black lid just behind the Nixie tube).

This is a description of the design from Tony Duell:

HP made a decade counter/display board where the counter flip-flops were made from pairs of transistors in the conventional way (8 transistors on the board). These were controlled with diodes to count in 1242 (not 1248) BCD code.

The outputs of these counters drove 8 neon bulbs, and by varying the bias applied, the state of the counter could be latched in the bulbs (that's why this is relevant here). These bulbs were mounted inside a plastic block on the PCB, and shone onto a thick-flim circuit of CdS photoresistors. These were connected to form a binary to decimal decoder to drive a nixie tube.

Inside [the block] there are 8 neons. From the top, they are : C, C/, B/, B, D, D/, A, A/ (according to the manual). The neon wires are soldered to the PCB. On top of the block is the thick-film LDR array, and on top of that is a resistor network of 10 270k resistors. The top wire of that goes to the +20V rail, the wires on the left go to the nixie cathodes (there's a 270k resistor from each cathode to +20V). The LDRs also connect to the cathodes. The bottom wire from the resistor network is not used, but the pin it's connected to is the common of the LDR array, and goes to -130V.

I can provide a pinout of the 15 pin card edge, but the signals may not be too obvious without the complete service manual. Pin 1 is towards the front (nixie tube) end

1 : -130V
2 : 
3 : 
4 : +170V
5 : Transfer Input (latch enable)
6 : BCD Output A
7 : Signal Input
8 : Gate Input (Not used?)
9 : BCD Output B
10 : Signal Output to next decade
11 : +20V 
12 : Reset Input
13 : BCD Output C
14 : BCD Output D
15 : -15V

And from Dave Brown, regarding model numbers:

The DCAs (Decimal Counter Assembly) in those counters (5243 series, 5245 series) came in low and high speed versions. The -6016 is the normal low speed 600kHz version used in most of the count positions and provides +1224 BCD output to the rear panel connector. The -6003 version is the option 03 variation of it that provided 1248 BCD output with the '1' state negative.(as opposed to the -6002 which was the same but with '1' state positive.)

This module was used in several pieces of HP test equipment, including the 5245L frequency counters.

You can see more photos by clicking here.

Does anyone recognize these tubes, and better, have a datasheet for them?

I received the following information via e-mail:

Those are single-digit vacuum fluorescent displays. "ISE" is a subsidiary of Noritake-Itron:

http://www.noritake-elec.com/itron/

Two wires are the filament connections (takes 1.5V, AC or DC), one is the control grid, and the remaining two are the symbol anodes (negative sign & overflow indicator), which should be biased at +25 to +35 volts DC w.r.t. either filament connection, through current-limiting resistors (10k or so).

• Casio 121-B, AS-L and FX-1
• Commodore 512
• Marchant I
• Monroe 610, 1655, 1710, 1770, 1775
• SCM Cogito 412, 414
• Sharp CS-363R
• Silver Reed SE-702
• Singer Friden 1114, 1118
• Sony Sobax ICC-400W, ICC-500W
• Remington-Rand 1259S

The main calculator page is here.

You can read a review of this counter here.

This is an eight-digit, 120 MHz counter.

You can read a review of this counter here.

This is an eight-digit, 180 MHz counter with phase-locked multiplier.

Quantity five. This is a neat little 2.5 digit multimeter.

The following two scanned pages are from the "TEST AND CALIBRATION" chapter of the manual.

[Medium]   [Large]

[Medium]   [Large]

I've scanned parts of the Operating and Service Manual:

Calibration

• Calibration section, page 1
• Calibration section, page 2
• Calibration section, page 3
• Calibration section, page 4

Troubleshooting

• Troubleshooting Tree
• Maintenance section, page 1
• Maintenance section, page 2
• Maintenance section, page 3
• Maintenance section, page 4
• Maintenance section, page 5

Diagrams

• Wiring Diagram
• Location of Chassis Mounted Components
• A1 Board Component Layout

Schematics
These images are in PCX format. The original schematics come as fold-outs in the service manual, and are too large for my flatbed scanner. Each page has been scanned as two parts, a left side and a right side.

• A1, Page 1, Left Side
• A1, Page 1, Right Side
• A1, Page 2, Left Side
• A1, Page 2, Right Side

Parts List

• A1 parts list, page 1
• A1 parts list, page 2
• A1 parts list, page 3

With 5252A Prescaler and 5265A Digital Voltmeter (plug-ins).

With 5253B Frequency Converter (plug-in).