ELL1

The ELL1 is a twin output pentode designed expressly for car radios. Philips Miniwatt’s 1940 publication specifies that application, with two systems for push-pull operation in one envelope. The manuals explain the choice in relation to the car battery: heater and plate currents were kept low, with relatively modest transconductance and a balanced circuit to use available power. The two cathodes connect internally to each other and the suppressors; screens also share a connection. The two plates and control grids remain separate.

Indirect heating requires 6.3 V and 0.45 A; the 1940 Philips sheet specifies parallel heater supply from a battery. For one system it gives plate and screen 250 V, control −19.5 V, plate current 15 mA, screen current 2.5 mA, transconductance 1.7 mA/V and plate resistance 110 kΩ. Its push-pull example, with common cathode resistor 560 Ω and 16 kΩ plate-to-plate load, gives 4.5 W at 3.5% total distortion with 19 V RMS drive per grid. Total plate current changes from 2 × 15 to 2 × 17 mA and screen current from 2 × 2.5 to 2 × 5 mA. Bias changes from −19.5 to −24.5 V at maximum signal: circuit and full-signal values matter as much as the designation.

Manual versions do not all give the same application point. The Dutch chapter, pages 50–52, gives 5.4 W at 3.7%, plate and screen 250 V, common cathode resistor 600 Ω, plate-to-plate load 16 kΩ and drive 19 V RMS per grid. It then considers a plate source with 1.6 kΩ internal resistance and other stages drawing 20 mA: the corresponding example, again with cathode resistor 600 Ω and load 16 kΩ, gives 4.75 W at 3%, with 18 V RMS per grid. Figures belong to their respective circuits and must not be merged into a single performance claim.

The attention to supply is practical. Manuals describe the car-radio vibrator, transformer and filter as a source with appreciable internal resistance that changes operation under load. They also mention battery-voltage variations during charging. Philips’s ordinary 1940 limits per section are plate 250 V, screen grid 275 V, plate dissipation 4.5 W, screen dissipation 0.7 W without signal and 1.5 W at maximum signal, cathode current 30 mA. Heater-cathode permits 50 V DC or AC RMS and maximum external resistance 5 kΩ; the 1940 sheet gives maximum grid resistor 3 MΩ. The 550 V cold plate and screen ratings are separate limits, not normal operating voltages.

The base is European eight-side-contact type. The drawing distinguishes two plates, two control grids, heater contacts and common screen and cathode/suppressor connections, with metallization marked m. It is not a bottom-pin octal base. Philips gives maximum bulb diameter 42 mm and maximum overall height 100 mm; base diameter is separately marked 35 mm. These dimensions are not interchangeable. Documentation: Philips Miniwatt, ELL1, August 1, 1940 sheets, four pages; chapters ELL1 Doppelendpenthode and ELL1 Double Output Pentode, pages 134–136; Dutch ELL1 chapter, pages 50–52. Editions are retained separately without automatically treating the sheet year as the introduction date.