EK90 = 6BE6, 5750, 6H31 tube Radioröhre

EK90 / 6BE6 heptode for audio modulators and DIY effects

The EK90 is a compact pentagrid converter whose multiple grids allow two signals to interact inside one valve system. Beyond its original frequency-converter role, this structure supports modulators, tremolo, experimental gain control and creative audio effects.

Its transfer characteristic was developed for mixing rather than neutral preamplifier service. That intentional non-linearity can be useful in studio effects, synthesisers and guitar circuits where controllable colour and signal interaction are desired.

Suitable applications

• Amplitude modulators and experimental audio mixers
• Tremolo and ring-modulator-style effects
• Controllable distortion and tone-shaping circuits
• Service of classic AM mixer and oscillator stages

Technical specifications

Valve type

Pentagrid converter heptode

Equivalent designations

6BE6, 5750 and other manufacturer-dependent equivalents

Base

Miniature B7G, 7-pin

Heater

6.3 V at 300 mA

Typical converter condition

Va 250 V, Vg2/g4 100 V, Vg3 −1.5 V and Ia approximately 3 mA

Screen current

Typically approximately 7.1 mA

Conversion transconductance

Approximately 0.475 mA/V

Internal resistance

Approximately 1 MΩ

Anode dissipation

Approximately 1.1 W maximum, depending on manufacturer data

Dimensions

Approximately 18 mm in diameter and 47 mm body height excluding pins

B7G connections – bottom view

Pin 1

Oscillator or control grid g1

Pin 2

Cathode and suppressor grid g5

Pins 3 and 4

Heater

Pin 5

Anode

Pin 6

Screen grids g2 and g4

Pin 7

Signal control grid g3

Audio experimentation notes

One signal may be applied to g1 and a second signal or control voltage to g3. The resulting characteristic is useful for mixing and modulation, but normally produces more distortion than a conventional audio triode unless suitable linearisation is employed.

The EK90 and EH90 have a similar connection arrangement, but their grid geometry and characteristics differ. Substitution in a compressor or modulator therefore requires a revised bias condition.

Questions about selection and audio use

Is the EK90 suitable for creative audio and guitar effects?

Yes, its two controlling grids support modulation, tremolo, controllable distortion and unusual mixing functions. This makes the affordable EK90 particularly attractive for experimental effects, synthesisers and characterful guitar circuits.

Can the EK90 be used in a circuit inspired by Blöhbaum's MTA principle?

Yes, as an inexpensive multi-grid valve it can provide a useful starting point for original transconductance and multiplier experiments. The published MTA circuit uses separate triode and hexode sections, so an EK90 version requires an additional active device and a complete redesign.

Can the EK90 be used as a 6BE6 or 5750?

Yes, the EK90, 6BE6 and 5750 are corresponding designations within this pentagrid-converter family. The individual manufacturer's ratings, heater data and equipment operating point should still be checked before installation.