EF41 — Small Signal Pentode, Rimlock | Tubeofile | Tubeofile

EF41

Name: EF41
Brand: Philips

Small Signal Pentode — Rimlock — Philips

Data: HighHigh quality — base, heater, all universal parameters present, and ≥50% of desirable parameters filled in. Safe to use for design decisions.

↗ r-type.org ↗ TDSL ↗ Radiomuseum

Known Equivalents & Substitutes

6CJ5CV3886HF61W1507F1662VP

Similar Tubes (Not Drop-In Compatible)

EF40

Same Rimlock B8A base and same heater, but sharp-cutoff AF pentode vs variable-mu RF/IF pentode — different gm/ra characteristics and intended application; not a drop-in substitute without circuit redesign

EF85

Successor variable-mu RF pentode with similar characteristics but on Noval (B9A) 9-pin base — not pin-compatible with Rimlock

EF89

Successor variable-mu RF pentode with improved characteristics but on Noval (B9A) 9-pin base — not pin-compatible with Rimlock

Electrical Specifications

Absolute Maximum

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

Screen Voltage (max)Screen Voltage (max, Ia=6mA uncontrolled)125V

Anode Dissipation (max)Anode Dissipation (max)2W

Screen Dissipation (max)Screen Dissipation (max)0.3W

Notes

Variable-mu (remote cutoff) characteristic: gm drops to 1/100th of its maximum value when Vg1 is reduced from -2.5 V to -39 V. This makes the EF41 suitable for AGC-controlled IF/RF stages.
Internal metal shield encloses the entire electrode system — no external screening is needed, but the valve must be pressed firmly into the holder and the retaining lugs on the raised metal edge of the socket must be bent slightly inward to ensure proper shield contact.
Screen grid voltage is derived via a series resistor (Rg2 = 90 kΩ) from the anode supply; screen voltage at the valve is approximately 100 V at the standard operating point (Vb = 250 V, Ig2 = 1.7 mA).
The Vs_max limit is operating-point dependent: 300 V when Ia < 3 mA (cut off by AGC), 125 V when Ia = 6 mA (normal uncontrolled condition).
Rg1_max = 3 MΩ applies when grid bias is obtained by means of a cathode (biasing) resistor. The separate Rfk_max = 20 kΩ limit applies to the external resistance between heater and cathode.
HF61 is the French Mazda designation, W150 the British Osram/GEC designation, 7F16 the French Mazda numbering, 62VP another European designation, and 6CJ5/CV3886 the JETEC/UK military designation — all electrically and pin-identical.
EF40 (Rimlock AF pentode) and EF41 share the same base but are not interchangeable: EF40 is a sharp-cutoff audio pentode while EF41 is a variable-mu RF/IF pentode. Circuit constants differ significantly.

Pin Layout — Rimlock

1Heater

2Anode

3Internal Connection

Socket-Compatible Tubes ⚠ Not electrically compatible

EL41 EL42

References