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.
Looking across the anode. The grid can be seen at either end beyond the anode. At the right side of the image the twin filament strands and their tension springs can be seen.
The additional lettering on the glass.
The thin glass tube envelope is 10 mm in diameter, and excluding the B8D base wires is 44 mm tall.