6AK6S

The 6AK6S is a miniature power pentode in the Mazda-Belvu Five Star series, presented by CIFTE as an RF amplifier. The source states characteristics similar to the 6AK6 and construction intended to withstand shock and vibration in mobile equipment, particularly aeronautical and industrial applications. The heater is specified for at least 5000 successive on/off cycles: a heating-cycle requirement, not a 5000-hour life or a general guarantee under every operating condition.

The cathode is indirectly heated. The heater, intended for parallel supply, requires 6.3 V, 150 mA; permitted voltage range is 5.7–6.9 V. The document uses the hybrid rating system: maximum plate voltage 300 V, screen 275 V, plate dissipation 3 W, screen dissipation 0.8 W, cathode current 21 mA. Control and suppressor grids have an upper limit of 0 V. Further limits are heater–cathode 180 V, control-grid circuit resistance 0.5 MΩ, hottest bulb spot 165 °C.

The nominal point uses plate and screen 180 V, suppressor 0 V, control grid −9 V. Plate current 15 mA, screen current 2.5 mA, transconductance 2.25 mA/V, internal resistance 0.2 MΩ. The class A1 amplifier table uses these voltages and no-signal currents, a 10 kΩ plate load and 9 V peak input: output is 1.1 W at 10% total distortion. Its note requires a direct socket connection between suppressor pin 2 and cathode pin 7.

Unshielded capacitances are control grid–plate 0.12 pF, input 3.6 pF, output 4.2 pF. Curves cover plate characteristics, power and distortion versus load, and operation with screen tied to plate. That is a separate arrangement, not the preceding pentode point. The load graph separates total, second-harmonic and third-harmonic distortion; the A1 table’s 10% remains tied to its 10 kΩ load. The sheet also specifies maximum unpressurised altitude 18 km, retained in its aeronautical context.

The seven-pin base is designated 7C10: control grid 1, suppressor 2, heater 3 and 4, plate 5, screen 6, cathode 7. Any mounting position is allowed. The drawing distinguishes maximum diameter 19 mm, maximum height above the pin seating plane 47.6 mm, maximum pin projection 7.14 mm; these are not added into an unquoted overall height. Documentation: CIFTE, Mazda-Belvu, 6AK6S, Pentode de puissance – Amplificateur R.F. – Sécurité “Cinq Étoiles”, edition marked 1-68, seven file pages, one blank.