6F6S

Power Pentode — Octal

Known Equivalents & Substitutes

6F66F6GT6F6GCV1542VT-66

Similar Tubes (Not Drop-In Compatible)

2A5

Same electricals but UX6 base (6-pin) — not pin-compatible

42

Same electricals as 2A5/6F6 but UX6 base with different heater (6.3V, 0.7A)

6P6S

Soviet 6V6 equivalent — beam tetrode vs pentode, different operating characteristics

Electrical Specifications

Section 1 — Pentode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)375V

Screen Voltage (max)Screen Voltage (max)285V

Anode Dissipation (max)Anode Dissipation (max)11W

Screen Dissipation (max)Screen Dissipation (max)3.75W

Max Grid ResistorMax Grid Resistor (self-bias)

Notes

Cyrillic designation: 6Ф6С. Russian_equivalents.json confirms: 6F6S ≈ 6F6GT.
From Tung-Sol datasheet: pentode connection at Va=250V, Vs=250V: Ia=34mA, gm=2500 µmhos, ra=80kΩ, Pout=3.2W. Triode connection at Va=250V: Ia=31mA, gm=2600 µmhos, ra=2600Ω.
Maximum ratings (pentode): Va_max=375V, Vs_max=285V, Pa_max=11W, Ps_max=3.75W.
Grid resistor: max 0.5MΩ for self-bias, 0.1MΩ for fixed bias.
The 6F6/6F6GT/G, 2A5, and 42 are all pentode power amplifiers with identical electrical characteristics — only heater and base differ.

Pin Layout — Octal

1No Connection

2Heater

3Anode

4

Socket-Compatible Tubes ⚠ Not electrically compatible

References