The DC70 was designed for use in UHF communications equipment. The data-sheet talks of 'push-to-talk' equipment. In common language the 'walkie-talkie'. So as not to fail to transmit the first word the filament is overrun and thus if operated in continuous fashion the service live of the valve would be very short, in fact even in PTT service the life is estimated at 200 hours.
The lettering on the glass seems to be 4.1R9L1
The top of the envelope: the coated filament attached to two tension springs. The copper grid supports are substantial.
The base: the filament supports are plates that act as shields. The anode is two sided and the lower strap can be seen.
The whole valve: the anode is flat and here seen diagonally at the bottom of the image.
The thin glass tube envelope is 10 mm in diameter, and excluding the B8D base wires is 42 mm tall.
