E80F

The E80F, also listed as 6084, is a Philips special-quality pentode for amplification in professional equipment. The sheet highlights low cathode interface resistance, mechanical robustness and gold-plated pins on its Noval base. Production samples undergo a 10,000-hour life test against defined end-of-life values: this is a qualification criterion, not a promise that every individual tube will last exactly that long.

The indirectly heated cathode uses a 6.3 V, 300 mA heater supplied by AC or DC. At Philips' nominal point, with 250 V plate, 100 V screen, suppressor grid at 0 V and a 550 Ω cathode resistor, plate current is 3 mA, screen current 0.65 mA and transconductance 1.85 mA/V. The stated internal resistance is 1.5 MΩ. The absolute limits of 300 V plate and 200 V screen do not describe this operating point.

Philips also gives a resistance-coupled audio amplifier. In the 1968 sheet, with plate and screen supplies of 250 V, plate resistor 0.22 MΩ, screen resistor 1.2 MΩ, cathode resistor 1.5 kΩ, grid resistor 1 MΩ and next-stage load 0.68 MΩ, gain is 175. Output is 25 V RMS where positive grid current reaches 0.3 µA, with 1.4% total distortion. A separate application is electrometer service: heater 4.5 V, plate and screen 40 V, suppressor 0 V and control grid −2.15 V. At that point plate current is 40 µA and maximum negative grid current is 10⁻¹⁰ A.

On the Noval base, the screen is pin 1, internal shields pins 2 and 7, cathode pin 3, heater pins 4 and 5, plate pin 6, suppressor grid pin 8 and control grid pin 9. Special quality includes shock and vibration tests on samples, which are not normal operating conditions. Philips warns that average heater voltage outside 6.0–6.6 V shortens tube life.