EF86

EF86 has no equivalent designation confirmed by the archive. Completed sales put the typical price at $39.50 per tube.

The EF86 is a low-frequency pentode intended primarily for input stages of low-frequency amplifiers where low microphony and low hum are required. It has an all-glass miniature envelope with a nine-pin base, and its screen grid and internal shield are brought out to separate base pins.

Construction

The EF86 uses indirect heating with parallel supply, operable from AC or DC. The heater requires 6.3 V at 0.2 A. The base type is S 9/12 per ČSN 35 8904. The maximum weight of the tube is approximately 15 g.

Ratings

Maximum ratings include an anode voltage of 300 V, anode dissipation of 1 W, screen-grid voltage of 200 V, screen-grid dissipation of 0.2 W, and cathode current of 6 mA. Cold anode and screen-grid voltages may reach 550 V. The maximum voltage between cathode and heater is 100 V when the cathode is positive and 50 V when the cathode is negative. The maximum external resistance between cathode and heater is 20 kΩ, or 120 kΩ when the EF86 is used directly as a phase inverter before the output stage.

The maximum control-grid circuit resistance depends on bias conditions: 3 MΩ with cathode-resistor bias and anode dissipation of at least 0.2 W; 10 MΩ with cathode-resistor bias and anode dissipation less than 0.2 W; and 22 MΩ with bias via grid current and zero cathode resistance. The grid voltage at which grid current starts is -1.3 V maximum.

Capacitances

Input capacitance is 3.5 pF, output capacitance is 5 pF, grid-to-anode capacitance is less than 0.05 pF, and control-grid-to-heater capacitance is less than 0.003 pF.

Typical Operating Characteristics

At an anode voltage of 250 V, with a screen-grid voltage of 140 V and a control-grid bias of 2 V, typical values are anode current 3 mA, screen-grid current 0.5 mA, transconductance 2 mA/V, amplification factor 38, and internal resistance 2.5 MΩ.

Replacements

The datasheet states that the EF86 can replace the foreign types 6BK8 and 6267, and can replace older types EF12k and EF40 after a base change.

Per-tube prices from completed sales, 2024-01-15 to 2026-09-05. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for EF86, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

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3 further designations appear alongside EF86 in the literature but below the evidence threshold used here, so they are not listed as equivalent.