Sensibly equivalent¶ to:
The DER triode design rom Marconi dates from 1921. The filament is thoriated tungsten and so emission is achieved at a lower temperature than with pure tungsten, hence the description dull emitter. The construction is of a cylindrical anode with a helical grid passing through it, that in turn is threaded by the filament.
The balloon envelope is 43 mm in diameter and, excluding the B4 pins, is 80 mm tall.
Reference: 1003. Type DER was first introduced in 1921. See also 1921 adverts.
Absolute Maximum Operating Conditions¶
Updated May 16, 2015.