C142

The Philips Miniwatt C142 is a screen-grid tetrode for high-frequency amplification. Our historical sources place it in 1927. Both examined Philips sheets stress a special AC filament while retaining direct heating: 1 V, 0.25 A. AC filament operation therefore does not imply a separate cathode. The detailed leaflet particularly specifies Philips receiver 2501.

The catalogue sheet “Voor wisselstroomvoeding”, page 38, gives anode voltage 50–150 V, auxiliary-grid voltage 25–75 V, amplification factor 150, transconductance 1 mA/V, internal resistance 150 kΩ and normal anode current 4 mA. Saturation current 20 mA is separate, not assumed to be normal permissible current. The text references A442 construction and praises amplification/selectivity with correct use; this does not establish electrical interchangeability.

The leaflet “Philips Wisselstroomlamp Miniwatt C142” retains those anode/screen voltage ranges but gives transconductance 0.8 mA/V, negative grid bias 1.5 V and normal anode current 1.7 mA. Anode-grid capacitance is 0.01 µµF, equivalent to 0.01 pF. The catalogue instead gives 0.05 cm; that historical unit is retained without substituting a conversion not stated in the document. The copies do not establish the revision sequence; both characteristic sets remain separate.

Both sheets include anode current versus grid voltage curves at anode 150 V/screen 75 V or anode 100 V/screen 50 V. They explain tetrode operation without making the amplification factor or axis extent a guaranteed whole-receiver gain. The detailed leaflet also ties good behaviour to correct use, including an oscillating detector: a period application description, not a circuit-independent guarantee.

Dimensions differ too: catalogue maximum length 110 mm/diameter 39 mm, detailed leaflet 102/45 mm. Neither length line states the pin datum; records retain that limitation. The leaflet specifies base A35 and base width 35 mm, showing four lower contacts and a screw top connection in the valve illustration. No sufficiently defined contact numbering is supplied to construct a pinout here; orientation must follow the original drawing. Documentation: Philips Miniwatt C142 Voor wisselstroomvoeding, page 38; Philips Wisselstroomlamp Miniwatt C142, one-page Dutch leaflet, illustration, A35 base and curves. No explicit publication date in the examined copies.