ITT / STC: Numerical Indicator Tubes.

GN4A, 5A, 6A.
Numerical Indicator Tubes
Types: GN4A, GN5A, GN6A
(Suffix 'A' denotes clear bulb).

Note the background material: Could that really be genuine wood-effect Fablon?

Abbreviations: dp = decimal point, LH = left hand, RH = right hand. Char. = character, Rec. = recommended,
Maint = maintenance. HT = High Tension (ie., B+), extn = extinction, avg = average, pk = peak.

Type No.
Bulb colour

Char Height
Min HT
Max extn. V


Cathode current /mA
Base & view.
Rec. min. max min rec max avg max pk.
GN4 Red 01234
 0.6 170 100 74 100 1.5   3.0 10 B13B
end view
GN4A Clear
GN4P Red 01234
LH dp
GS4 Red A V Ω + - % ~
GS4A Clear
GN5 Red 01234
 1.0 200 100 75 110 2.5   5 10 B12A
end view
GN5A Clear
GN6 Red 01234
 0.55 200 115 75 110 1.25   2.5 9 Wire end.
Side view
GN6A Clear
GS6 Red - + ~  0.35
GNP-7 Red 01234
LH dp
RH dp
 0.61 170 100 60 110 1.5
(dp 0.1)
2 3
(dp 0.5)
(dp 4)
Wire end.
Side view
GNP-7A Clear
GNP-7H Red 180 110 25 100   25
(dp 6)
GNP-7AH Clear

Notes from the 1971 data sheets:
1a) The highest supply voltage available should be used with a suitable anode series resistor.
1b) For long life expectancy it is recommended that the discharge should be sequentially stepped from one cathode to another. This normally occurs in most conditions of operation, but where a static condition is encountered, it is desirable to step the discharge at least once in 100 hours.
1c) For a.c. operation it is recommended that a 240V r.m.s. supply be applied via a Q8/5 rectifier [miniature Selenium type: 340 PIV, 5mA] and a resistor A in series. A 390K resistor should be connected in parallel with the indicator tube and resistor A.



Resistor A




2) Pre-bias voltage is that between the operating and non-operating cathodes. At the lower values of pre-bias, current to the non-operating cathodes is increased and the legibility of the display will be impaired by background haze. A minimum pre-bias of 35V is recommended for the GNP-7H and GNP-7AH models and 80V for the GNP-7 and GNP-7A models. Although lower values are not injurious to the indicator tubes, the equipment designer should reach the best compromise between display quality and drive circuit cost. The maximum pre-bias voltage is set to avoid non-operating cathodes acting as auxiliary anodes.
3) Note: If an indicator tube is operated with the bulb temperature below 0°C, there will be an increased variation of characteristics and the life of the tube will be shortened.
For D.C. Operation where wide temperature variations occur, a high value of supply voltage, together with an anode series resistor of the appropriate value, should be used.

STC Mechanical Data:
GN4 physical data.

GS6 (Symbols + - ~ ): Same bulb dimensions as GN6. Display Area 0.35 x 0.35" (8.9 x 8.9mm).

Character Height: 15.5mm
Bulb Diameter: 19.1mm max.
Weight: 7.6g (0.24 oz.)
Operating temp range: -20 to +70°C

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