DDD11

The Telefunken DDD11 is a directly heated battery double output triode for class B. Two systems in one envelope provide the documented push-pull operation. Filament nominal 1.2 V, 100 mA. A single dry cell is allowed from usual initial voltage down to 0.9 V; other sources, accumulator or mains, require stated ±15% tolerance. All voltages refer to the negative filament end.

The document describes operation with DC11 driver triode and 2:1 step-down driver transformer. Plate supply 120 V, DDD11 grids −4.5 V, plate-to-plate load 14 kΩ: output 1.4 W at 10% distortion criterion. At 90 V, bias −3 V, same load: 0.6 W. The note ties performance to DC11 operation; graphs give distortion of DC11 plus DDD11, not independent of drive.

The table gives plate currents 2 × 1.5/2 × 1.4 mA, and at full drive 2 × 9/2 × 5.5 mA. The full-drive row also prints Ruhestrom, idle current, an inconsistent label not used to define another idle rating. The 3.5/2.5 V RMS inputs are applied to the DC11 grid, not directly to DDD11 grids. DC11 bias is separately −4.5/−3 V. Distinguishing measurement points prevents an unsupported output-tube input sensitivity.

Listed limits: filament 1.4 V with source footnote, cold plate voltage 200 V, operating plate 150 V, mean cathode current 12 mA. Cold voltage is not normal operating voltage. Plate curves are per system, grid parameter, with load lines for 120/90 V and 14 kΩ plate-to-plate. Two further graphs show currents, DC11 input requirement and distortion against output. Axis ends do not become extra guaranteed limits.

The base belongs to German steel Y8A in archive information. Primary diagram is unnumbered: both plates/grids, filament ends and metal coating, with multiple negative-reference contacts. Functional arrangement retained without invented numbering. Drawing dimensions: body diameter 36 mm, base diameter 43 mm, height above base bottom plane 43.5 mm, not marked maximum; lower projection 15.5 mm and key diameter 10 mm separate. Weight explicitly maximum 50 g. Documentation: Telefunken, DDD11, Doppelendtriode für B-Verstärkung, four technical pages from December 1941/March 1942, with later collection index. Index date is not tube manufacture.