The WR1 from Cossor dates from 1924 and is a dull emitter triode with a built-in filament resistance of 8 Ohms. The filament is oxide-coated.
Cossor had introduced dull emitter replacements for their earlier valves in the form of the W1 and W2. This valve was made to ease the transition from the six volt filament supply for bright emitter sets to the two volt LT supply for the dull emitter valves. The advertising literature stated that when all the bright emitters had been replaced, the screw could be moved and the set immediately operated on the more economical two volt accumulators.
In the groove in the brown composition hidden under the black insulation is the wire to form the 8 Ohm dropper resister. The screw in the position as shown shorts out the resistor for two Volt operation. With the shorting screw placed in the dummy hole to the right, the resistance is activated and a six volt supply is required.
The anode dome is identical to the original bright emitter triodes the P1 and the P2.
The wide glass tube envelope is 29 mm in diameter and, excluding the B4 base pins, is 77 mm tall.
Reference: 1003. Type WR1 was first introduced in 1924.