EF86

Soviet 6Ж32П version of the EF86.

EF86 is a miniature high gain, low mu, pentode vacuum tube. It has 9 pins and connects to a B9A base.

The EF86 was introduced in the late 1950s and were produced by Philips, Mullard, Telefunken, Valvo, and GEC among others. It is very similar to the octal base EF37A and the Rimlock base EF40, and was used in many preamplifier designs during the last decades of vacuum tube hi-fi development. An industrial variant of the tube is known as 6267. In the former Soviet Union a variant was also produced as type 6Zh32P (Russian: 6Ж32П.) Currently EF86 are being produced in Russia in two versions under Electro-Harmonix brand and in the Slovak Republic under JJ Electronics brand name (former Tesla).

Characteristics

6.3 Volt, 200 mA indirected-heated A.F. Pentode in a Noval (B9A) base with an EIA 9CQ (or 9BJ) basing diagram.

• Transconductance: 2.2 mA/V at I_a=3.0 mA, I_g2=0.6 mA, V_a=250 V, V_g1=-2.2 V, V_g2=140 V, V_g3=0 V
• Voltage gain: 185 (45dB) at V_supply=250 V, I_k=0.9 mA, R_k=2.2 kilohm, R_a=220 kilohm, R_g1=1 megohm, Vout<44 V_RMS

Maximum Ratings:

Plate voltage, Va      < 300 V
Anode dissipation, Wa  <1.0 W
Screen voltage, Vg2    < 200 V
Cathode current, Ik    < 6 mA

Special precautions have been taken in the design to reduce:

• mains hum (through a bifilar-wound twisted pair of heater wires),
• noise, and
• microphonics (through a rigid internal structure to reduce resonances).

Compared to other pentodes, the EF86 is generally much quieter, but compared with some triodes, the noise (about 2 µV equivalent input noise to 10 kHz) is slightly higher and the microphonics (especially in instrument amplifiers) can be a problem even when mounted in a vibration-reducing valve holder (although it was regularly used in tape recorder input stages, for example).

Similar Devices

• 6267 * Z729 * CV2901 * 6BK8 * 6CF8 * 6F22 * CV8068 * CV10098

Special Quality:

• EF86SQ * M8195 * CV4085 * EF806S

Different heater voltage/currents:

• PF86 (4.5 V/300 mA)
• UF86 (12.6 V/100 mA)

Further reading

[1] Tubeworld.com's EF86 page.

[2] Mullard's EF86 at the National Valve Museum.

[3] The Mullard EF36, EF37 and EF37A at the National Valve Museum.

[4] TDSL Tube data: EF86.

[5] Datasheet for Thorn/Mazda 6F22/EF86 (pdf).