EDD11

The EDD11 is a twin output triode for class B push-pull amplification. Philips’s 1938 sheet describes car-battery heater supply and an EBC11 driver. The triodes have separate plates and grids but a common cathode; the metal envelope connects to the cathode reference. Telefunken’s circuit shows an interstage driver transformer and a plate-to-plate output transformer feeding the load. The twin triode and driver therefore form a system: published performance does not belong to the bare tube without its circuit.

Indirect heating requires 6.3 V and 0.4 A; Philips specifies parallel heater connection to the battery. Philips and Telefunken tables give two points: plate 200 V, plate-to-plate load 12 kΩ, output 4.5 W at 10% distortion; plate 250 V, load 16 kΩ, output 5.5 W also at 10%. EDD11 grid bias is −6.3 V in both. Idle plate current changes from 2 × 1.6 mA at the first point to 2 × 3.5 mA at the second; at full modulation both give 2 × 17.5 mA. Low idle current and growth with signal are part of this documented class B output behavior.

Drive figures must be assigned to the correct tube. The listed 4.5 V RMS for maximum output is applied to the EBC11 grid, not directly to EDD11 grids. The EBC11 uses cathode resistor 1.6 kΩ and bias −6.3 V at 200 V, −8 V at 250 V. Philips writes driver-transformer ratio 3:(1+1), identifying its split secondary; Telefunken summarizes it as 3:1. EDD11 grid-drive power at full modulation is 0.1 W. Listed sensitivity 0.15 V RMS at the driver grid instead corresponds to only 50 mW output, not sensitivity for 5.5 W.

Declared maxima include operating plate voltage 250 V, cold plate 550 V, dissipation 3 W per plate and cathode current 25 mA per section. Maximum heater-cathode voltage is 50 V and external resistance 5 kΩ. Plate dissipation 3 W is not circuit audio output. Telefunken curves separate plate and grid currents as voltage changes and show drive requirement and distortion of the EBC11–EDD11 combination. They matter because grid drive here is more than a voltage supplied without current.

Construction uses a German eight-contact base with central key. Primary drawings distinguish two plates, two grids, heater and common cathode-envelope connection; one contact has no indicated function. Dimensions retain their maker: Philips maximum metal diameter 36.5 mm, maximum flange width 43.5 mm and maximum height above base plane 43.5 mm, excluding projecting contacts and guide. Telefunken draws metal diameter 36 mm, flange 43 mm and height to base plane 42.5 mm without marking these as maxima; maximum mass is separately 60 g. Documentation: Philips Miniwatt, EDD11, tentative data December 1, 1938, four pages; Telefunken, EDD11 Doppelendtriode für B-Verstärkung, 1938 sheets with conditions, circuit and curves. Dates identify publications, not manufacture of each specimen.