CL2

The CL2 is an audio output pentode developed for AC/DC radio receivers, with documented performance at reduced anode voltage. Indirect series heating is 24 V, 0.2 A; Philips explains the higher heater voltage by the requirements of this output valve. The historical 8 W designation concerns anode dissipation, while tabulated audio output reaches 3 W under specified conditions. Tungsram calls it TCL2 and highlights the top-cap control grid. The European base has eight side contacts and suppressor internally joined to cathode. Philips’ drawing of 4 July 1940 gives maximum height 123 mm and diameter 46 mm; Tungsram instead lists 109 and 42 mm for its version.

Philips’ 1940 point at 100 V anode and screen, 260 Ω cathode resistor and −15 V grid gives 50 mA anode, 8 mA screen, 3.8 mA/V transconductance and 16 kΩ internal resistance. With 2 kΩ load, output is 1.7 W at 10% distortion with 9.4 V RMS input. At 200 V anode and 100 V screen, cathode resistor is 420 Ω and grid −19 V: anode 40 mA, screen 5 mA, transconductance 3.1 mA/V, internal resistance 23 kΩ. A 5 kΩ load yields 3 W at 10% with 8.8 V RMS drive. Earlier catalogues also describe 200 V anode and 75 V screen, grid around −11 V, 40 mA anode and 4.5 mA screen: Philips gives 2.25 W at 10% into 5 kΩ with 6.9 V RMS drive. Each result must belong to its supply and load impedance.

Philips’ discussion of switchable receivers highlights a detail: changing between 110/127 and 220 V mains requires switching the output-transformer primary tap for the intended load. The unused portion must be disconnected, not shorted. The catalogue also describes 100 V screen at the 100 V anode point and 75 V at the 200 V point, retaining the same cathode-bias resistor in that circuit. Philips 1940 limits are 200 V anode, 100 V screen, 8 W anode, 1 W screen and 70 mA cathode; cold anode and screen 400 V. Grid leak is limited to 1 MΩ self-bias and 0.6 MΩ fixed bias; Tungsram and the earlier Philips catalogue instead specify 0.7 and 0.3 MΩ. Heater–cathode limit is 175 V peak with maximum external resistance 20 kΩ. These edition differences remain documented rather than becoming one merged specification.