▼ Menu


Sensibly equivalent to:
1M1 1M3 CV2980 Y25
See also:
Mullard DM70 Advert - Mullard DM70 contd. Advert
Extras ▼


The DM70 is a miniature tuning indicator designed for dry battery operation. The valve is badged as a Mullard product but also as made in Holland. This implies that it was in fact a Philips designed and built device.
The display changes from minimum to maximum for a 10 Volt change on the control grid.
The following comes from a Mullard data-sheet.
Battery receivers. The filament may be fed from a 1.4V battery or it may be connected in series with the filaments of other valves in the receiver, provision being made for a suitable shunting resistor if necessary. The operating conditions indicate which filament pin should be connected to the earthed side of the demodulator circuit.
Mains receivers. The filament may be fed from a 6.3 V heater transformer provided it is connected in series with a 220Ω, 1 W, 5% resistor. If the heater transformer has a centre-tap giving 3.15 V, a series resistor of 82Ω, 0.5 W,10% may be used. If desired, the filament, shunted by a suitable resistor, may be included in a series heater chain provided it also includes a current limiting device. With either form of connection in mains-operated receivers, pin 5 must be connected to the earth side of the demodulation circuit for satisfactory operation.
Construction etc. This valve is a triode in which the grid is in the form of a plate containing a tapered aperture. The anode is coated with fluorescent material which is viewed through the grid aperture. The length, L, of the fluorescent 'column' observed through the grid aperture decreases as the grid potential goes negative. The valve may be mounted in any position, the direction of viewing being indicated on the diagram of pin connections. Direct soldered connections to the leads of this valve must be at least 5 mm from the seal and any bending of the valve leads must be at least 1.5 mm from the seal.
The display travels within the keyhole shaped column.
The left hand diagram shows the glowing column when the grid is at filament potential. The right hand diagram shows the effect of making the grid several volts negative of the filament.
The thin glass tube envelope is 9 mm in diameter and, excluding the B8D base wires is 41 mm tall.
References: Datasheet, 1040 & 1043. Type DM70 was first introduced in 1952.


Pin Connections
B8D & B8D/F


Absolute Maximum Operating Conditions
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated August 01, 2019.
shape:thin.glass.tube construction:all.glass type:tuning.indicator age:1950.1960 base:b8d heater:1.4v pins:8 pin:1.g1 pin:2.ic pin:3.- pin:4.f pin:5.f pin:6.- pin:7.- pin:8.a
Return to Main Index