6BJ6 (=E99F) long life Pentode (close to CV3909, 6662, 7694)
Compact RF/AF tube for creative preamp builds
Socket: 7-pin Noval B7G; Uf 6.3V, If 0.3A
gm~4-5mA/V, Pa~1.7W; typical 250V/8-12mA
6BJ6 remote-cutoff pentode for gain control and audio DIY
The 6BJ6 is a compact variable-mu pentode with a gradual remote-cutoff characteristic. Its gain can be reduced progressively by applying a more negative control-grid voltage, making it useful for affordable preamps, gain-control stages and experimental tube compressors.
Its heater consumes only about 0.95 W, which is attractive in compact or multi-stage projects. The valve may be used at a fixed operating point or as a controlled-gain element in a purpose-designed circuit.
Suitable applications
- Affordable tube preamps and small-signal stages
- Variable-gain and automatic level-control circuits
- Experimental tube compressors and limiters
- Measurement, receiver and laboratory equipment
Technical specifications
- Valve type
- Remote-cutoff variable-mu pentode
- Equivalent designation
- CV3909
- Base
- Miniature B7G, 7-pin
- Heater
- 6.3 V at 150 mA
- Typical operating point
- Va 250 V, Vg2 100 V, Vg1 −1 V, Ia 9.2 mA and Ig2 3.3 mA
- Transconductance
- Approximately 3.6 mA/V
- Internal resistance
- Approximately 1.3 MΩ at 250 V
- Gain-control range
- At approximately −20 V on the control grid, transconductance falls to about 0.01 mA/V
- Maximum anode voltage
- 300 V
- Maximum anode dissipation
- 3 W
- Dimensions
- Maximum diameter approximately 19.1 mm and overall height approximately 54 mm
B7G connections – bottom view
- Pin 1
- Control grid g1
- Pin 2
- Cathode
- Pins 3 and 4
- Heater
- Pin 5
- Anode
- Pin 6
- Screen grid g2
- Pin 7
- Suppressor grid g3 and internal shield
Audio design notes
Compressor and gain-control applications require a suitable control voltage and a circuit designed around the valve's transfer characteristic. Short wiring, effective screen decoupling and a grid stopper support stable operation.
Safety notice: Despite its modest heater demand, the valve requires a correctly designed high-voltage supply and suitable protection against accidental contact.
Questions about selection and audio use
Is the 6BJ6 suitable for an affordable audio preamplifier?
Yes, its approximately 9.2 mA anode current and 3.6 mA/V transconductance can provide useful voltage gain in a purpose-designed small-signal stage. Its low heater current is also attractive for compact budget builds.
Can the 6BJ6 be used in a tube compressor?
Yes, its remote-cutoff characteristic allows gain to be controlled progressively by the control-grid voltage. This makes the valve interesting for experimental compressors, limiters and automatic level-control circuits.
Is the 6BJ6 useful for compact, low-power tube projects?
Yes, the heater requires only 6.3 V at 150 mA. This places a relatively small load on the heater transformer and makes the valve attractive for multi-stage or stereo projects.
Note: All brand names mentioned, such as Marshall, Fender, etc., are registered trademarks of their respective owners and are used here for descriptive and compatibility purposes only.
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Source: IHK Mittelfranken
Tariff Number: 85408100
Country of Origin: DE