NEW FOR 1953 A LOW HUM LOW-MICROPHONY PENTODE - THE EF86 -

The EF86 audio frequency pentode had been designed for use in high grade resistance coupled AF voltage amplification circuits.  - yes, this pentode was NOT designed as a TV valve as some ill informed naysayers would have you believe.

In such circuits any hum and microphony introduced by the valve must be kept to a minimum and the EF86 shows a maximal hum level of 5uV referred to the control grid.  This was achieved by using a bi-filar heater winding and careful internal screening, what, you thought that pin mesh screen was just for looks, oh no!  What's that I hear you say "Is he talking about the pin mesh anode?," well you may call it that due to the misnomer that has grown up within audiophile circles but the pin mesh bit is actually the screen.  

The pin routing were also carefully designed to minimise hum with the grid pin being placed equidistantly between the two heater pins such that the heater winding essentially had a centre tapped earth to balance out any residual hum.  The electrode cage had additional internal bracing specified within the design to enforce torsional rigidity to reduce intrinsic microphony.

The main characteristics of the EF86 are: -

Heater Voltage, Vf:.............................. 6.3V

Heater Current,  If:...............................200mA

Anode Voltage,  Va..............................250V

Anode Current,  Ia................................3mA

Hum Level...........................................<5uV

Mutual Conductance, gm.....................1.85mA/V

For more about this interesting landmark pentode, why not have a look at our EF86 product page where I write in a little more detail on uses for the EF86, especially for audio.