EF91

Small Signal Pentode — B7G

Philips

Known Equivalents & Substitutes

6AM6CV138Z778D36F12

Similar Tubes (Not Drop-In Compatible)

6AK5

Similar miniature RF pentode but different operating point and pinout (EF95 equivalent)

EF92

Lower gm variant (same envelope) — not a drop-in substitute due to different characteristics

Electrical Specifications

Section 1 — Pentode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)300V

Screen Voltage (max)Screen Voltage (max)300V

Anode Dissipation (max)Anode Dissipation (max)2.5W

Screen Dissipation (max)Screen Dissipation (max)0.65W

Cathode Current (max)Cathode Current (max)

Notes

Pin 2 is internally connected to grid 3 (suppressor) and the internal shield — must be grounded for proper operation and lowest noise.
Ri (internal resistance at g1) is approximately 1 MΩ — relevant for input impedance calculations.
μg2g1 = 70, indicating a high screen-to-grid-1 amplification factor.
Equivalent noise resistance Req = 1200 Ω at the typical operating point.
Noise resistance at 50 Mc/s: rg1(50Mc/s) = 7500 Ω.
Brimar rates Va_max at 275 V rather than 300 V (Philips); use the more conservative rating in designs requiring margin.
Triode-strapped data from Schlangen measurements: mu=70, gm=7.2 mA/V, ra=9.7 kΩ — high-mu triode characteristic suitable for high-gain voltage amplifier stages.

Pin Layout — B7G

1Control Grid (g1)

2Suppressor Grid (g3) + Internal Shield

3Heater

4

Socket-Compatible Tubes ⚠ Not electrically compatible

References