C405

The Philips Miniwatt C405 is a directly heated radio output triode. Filament 4 V, about 0.3 A; our historical sources place it in 1930. The German booklet compares it with B405, crediting higher permissible anode voltage/current and greater undistorted output. It describes sufficient room volume but says B443 provides greater volume with lower anode voltage and less preceding amplification. These are Philips application assessments in their period receiver context.

The trilingual table gives maximum anode voltage 250 V, normal anode current 20 mA, bias about −32 V, amplification factor 5. Normal transconductance 1.9 mA/V, maximum 2, normal internal resistance 2,600 Ω. Maximum anode dissipation 5 W. The supplement distinguishes Va0 maximum 400 V and VaL maximum 250 V, and maximum cathode current 25 mA. The 400 V is not presented as normal operating anode voltage, nor 5 W dissipation as useful loudspeaker output.

The German booklet gives another set: anode 100–200 V, factor 5, transconductance 2 mA/V, internal resistance 2,500 Ω; at 200 V normal current 12.5 mA with negative bias of 24 V. For undistorted reproduction it specifies negative bias 18 V at anode 150 V and 24 V at 200 V. This remains separate from the trilingual 20 mA/−32 V group. Heating may use a 4 V accumulator or AC, recommending Philips transformer 4009 for AC and Philips rectifier 506 for anode supply.

The supplement states output 1.1 W with 22 V RMS drive and anode load 5,200 Ω, without distortion percentage on that line. Grid-current onset −2 V with filament 4 V AC; maximum resistances Rg1 1.5 MΩ, Rg2 1 MΩ; capacitances anode-grid 4.8 µµF, anode-cathode 3.4, grid-cathode 5.3, equivalent to pF. Curves show current versus bias and anode families, one including the 5 W dissipation line. Axes extending to higher voltages do not increase the ratings.

Philips references base A32 and diagram S.I; the German drawing labels two filament F contacts, grid G and anode P without numbers or explicit viewing direction, base width 32 mm. Trilingual maximum overall length 91 mm, diameter 46 mm; German booklet length 92 mm excluding pins, diameter 45 mm. Dimensions retain their document and physical datum. The retained photo shows Philips Miniwatt marking and four lower contacts. Documentation: Philips Miniwatt C405, trilingual table, supplement and curves, four pages; Philips Miniwatt C405, German booklet pages 22–23. No explicit publication date in the examined copies.