D2F

The Philips Miniwatt D2F is a directly heated pentode for portable transceivers, chiefly transmission and audio modulation down to about 3 metres wavelength. Its filament requires 1.4 V at 0.24 A. The November 1940 booklet specifies parallel battery heating; the later English leaflet allows series or parallel filaments. It also describes triode-connected oscillation and receiver audio output. D1F filament currents must not be transferred to this valve despite their related construction and appearance.

Radial contacts and a hand grip permit replacement without opening the set; the version without the grip is D12F. Drawings identify anode, three grids, two filament ends and metallisation without numbering contacts. The English leaflet gives anode/screen 250 V, bias −5.5 V, anode current 10 mA, screen current 1.8 mA, slope 3.4 mA/V and internal resistance 0.5 MΩ. These describe one operating point, not every application’s currents.

For class C telegraphy the 18 November 1940 booklet uses two pentodes in push-pull at 3–5 metres. Anode/screen 250 V, control grid about −22 V and third grid zero give total anode current 24 mA, anode input 6 W, dissipation 3.6 W, useful output 2.4 W and efficiency 40%. Drive is about 29 V peak per grid. Pair currents and powers must not be assigned to each D2F; antenna efficiency is lower because circuit losses are excluded.

Combined anode/screen modulation with two class C pentodes uses anode 250 V, screen 130 V and a common 20 kΩ screen-feed resistor. At total anode current 20 mA the table gives input 5 W, useful output 1.6 W and efficiency 32%. Two triode-connected conditions, joining anode and grids two/three, are separate: telegraphy at 200 V with 1.7 W useful output, anode modulation at 180 V with 1.4 W. Drive and bias depend on connection; these are not generic-circuit guarantees.

For audio, one class A D2F at anode/screen 250 V, cathode resistor 465 Ω, bias −5.5 V and load 25 kΩ gives 1.2 W at 10% distortion with 2.8 V RMS input in the 1940 table. Quiescent anode/screen currents are 10/1.8 mA. Two in class AB at anode/screen 250 V, bias −7 V and load 20 kΩ give 3.4 W at 2.5% with 5.1 V RMS input; the English leaflet printed 5/45 instead states 3.5 W at 2.5%. Both remain attributed to their editions.

The 1940 limits include anode 250 V, anode dissipation 2.5 W, screen 250 V, screen dissipation 0.5 W without signal/1.5 W at maximum output, first-grid dissipation 0.15 W, first-grid current 3 mA and cathode current 20 mA. Zero-current ratings, anode 850 V and screen 450 V, are separate from operating limits. Cold anode-first-grid capacitance is below 0.03 pF. Curves show anode/screen currents, loading and distortion; axis extent does not enlarge tabulated ratings.

Both editions give maxima of 63 mm overall height with grip, 36.5 mm upper section and 19 mm upper diameter; contact-view widths are 24 and 32 mm maximum. Dimensions remain tied to their drawing sections. The English leaflet mentions removing small metallised areas to adjust input/output capacitance, a stated construction detail rather than external-appearance inference. Documentation: Philips Miniwatt D2F, trilingual booklet dated 18 November 1940, eight pages; Philips Miniwatt Special Valves, D2F/D12F, Valve for Portable Transceivers, B3.1 Eng., two pages, print 5/45, K833.