CBL1

The CBL1 combines two diodes and a high-transconductance output pentode with a common cathode for AC/DC receivers. The diodes can provide detection and automatic gain control; the pentode provides audio power amplification. Philips compares the output section with CL4, without making the complete valves identical. The heater requires 44 V and 0.2 A, with indirectly heated cathode and series connection. The base has eight side contacts and the pentode control grid is on the top cap. Philips and Mullard drawings give maximum height 130 mm and diameter 52 mm.

Philips’ manual describes the internal arrangement: the two diode anodes sit below the pentode on either side of the cathode, at the same height, with nearly semicylindrical shape. A screen separates the detector assembly from the output section. The top-grid connection helps reduce diode interaction and hum. The combination integrates receiver functions in one envelope but demands attention to the circuit: Philips permits automatic or semi-automatic bias and notes possible hum when audio amplification is inserted between diode and output stage. The sheet of 9 September 1953 limits intermediate gain to 15; the preserved German manual instead gives three. These are instructions from different documents, not one universal rule.

At Philips’ 1953 class-A point, anode and screen are at 200 V, cathode resistor is 170 Ω and bias approximately −8.5 V. Anode current is 45 mA, screen current 6 mA, transconductance 8 mA/V and internal resistance 40 kΩ. With 4.5 kΩ load, output is 4 W at 10% distortion with 5 V RMS grid drive. At 100 V anode and screen, the same table gives 0.85 W at 7%. The manual also devotes two tables to output-transformer voltage drop: with supply and screen held at 200 V, a 20 V drop brings the anode to 180 V; with load adjusted to 4 kΩ it lists 3.4 W at 10%. Obtained power therefore also depends on transformer and actual operating voltages.

For the pentode, Philips in 1953 gives maxima of 250 V anode and screen, 9 W anode dissipation and 70 mA cathode current. Permitted screen dissipation is 1.2 W without signal and 2 W at maximum output; grid-leak resistance must not exceed 1 MΩ. The 9 W is heat dissipated by the anode, not audio output. For each diode, the 1953 sheet gives 350 V peak inverse, 0.8 mA and 5 mA peak. The earlier Miniwatt sheet of 26 January 1938 and Mullard’s sheet instead give a 200 V diode-voltage limit. Heater-to-cathode limits also differ: 125 V in the 1938 sheet, explicitly DC or AC RMS, versus 175 V in the English manual. These differences require limits to remain tied to the specific manufacturer documentation.