DB3

The DB3 is a small Mullard medium-impedance triode with a directly heated 1.5 V, 70 mA filament. The original is a tentative-data sheet, not a final specification; that qualification accompanies both electrical points and construction drawing. Illustrated plate operation uses a few tens of volts, while the filament belongs to the small battery-tube family. The full designation matters: cathode-ray tubes beginning DB3 followed by further numbers are different types and do not supply data for this triode.

Two operating points are given. Plate 20 V, grid −1 V: plate current 0.5 mA, amplification factor 4.7, transconductance 0.35 mA/V, internal resistance 13,500 Ω. Plate 40 V, grid −2.8 V: current 1.8 mA, transconductance 0.62 mA/V, internal resistance 7,600 Ω; factor remains 4.7. The two columns’ conditions stay separate. These parameters describe the triode at those points, without alone defining equipment gain or output power.

Explicit limits are plate voltage 100 V and grid-circuit resistance 1 MΩ. No output power, distortion or characteristic curves are published; undocumented performance is not added. Similar designations do not establish electrical or mechanical interchangeability. The document examined specifically identifies DB3.

The drawing shows a two-ended filament, grid and plate with four-contact base. The grid uses the larger-diameter contact; the others are functionally labelled plate and filament ends, without pin numbers. The arrangement is preserved without arbitrary numbering or an unstated viewing orientation. Mullard maximum dimensions are 16 mm diameter and 69 mm overall height including pins. They apply to this documented version, without transferring DA3 dimensions. Documentation: Mullard, DB3, Medium Impedance Triode, Tentative Data, one page, printing reference 11238; no explicit date.