The DET1, designed around 1924, was the first dull emitter, thoriated tungsten filament transmitting valve, certainly in the UK, possibly in the world. It was a conventional triode with flat nickel anode, ribbed for strength and capable of dissipating a power of 35 watts at anything up to 1,000 volts. The cathode operated at 6 Volt, 1.9 Amp. The main frequency range was for Long and Medium Wave, that is below 2 MHz. Often the DET1 was used as a power master oscillator. Later in the 1920's a Short Wave version was developed that could operate down to 10 metres (30 MHz). The DET1SW was also made by Mullard as the 161D.
The valve had been a spare for a pre-war transmitter and came in a plain cardboard box that was lined with wadding as protection. The transmitters that it related to were the AD37 (1932) and the AD41 (1935).
The Saga of the Marconi Osram Valve gives the experimental type E 118 as a DET1 with heavy grid and anode leads, but does not give any reason for this.
The anode is supported by struts that clamp round the pinch stem. A glass tube is inserted into the stem and this carries the anode lead from the base to one of the anode supports. The other support carries a small getter carrier and this can be seen to the lower left of the picture.
The envelope carries the Marconi label and the DET1 was used in several pre-war transmitters.
A glass bead supported at the top by the grid supports and lower down to the pinch adds rigidity and also holds the filament tension spring.
Looking into the top of the envelope the anode cross section can be seen as well as the single inverted V of the thoriated tungsten filament and the grid wires. As the filament is thoriated tungsten it glows bright orange in use.
One of the anode supports in the foregrouns with the lower filament connects and grid.
The large L4 base with sprung pins screwed into the composition base.
An advert from Flight Magazine for the AD41.
The balloon envelope is 78 mm in diameter, and excluding the L4 base pins is 164 mm tall.
Reference: 1005. Type DET1 was first introduced in 1924.
Absolute Maximum Operating Conditions¶
Updated March 07, 2014.