6BJ6A

The 6BJ6A is a miniature variable-mu pentode for RF and IF amplification. Sylvania stresses low heater current, low input and output capacitances and relatively high transconductance. Tung-Sol presents it with the 6BJ6 as a remote-control voltage amplifier for applications needing low heater consumption. The distinguishing A-version feature is control of cathode interface-impedance formation.

Nominal heater supply is 6.3 V, 150 mA, AC or DC; heating is indirect and any mounting position is permitted. Sylvania’s preliminary sheet dated 22 August 1958 declares it identical to the 6BJ6 defined by EIA release 541A, except for interface-impedance control. The A suffix therefore does not mean a generic increase in power, gain or maximum voltage.

Sylvania describes a 500-hour life test with 6.9 V applied to the heater, other electrodes disconnected to simulate cutoff. Afterwards measurement uses 5.7 V heater, 70 V DC on plate, screen and suppressor, with control grid adjusted for 4 mA plate current. Maximum allowed interface impedance is 70 Ω. These voltages and duration belong to a qualification test, not normal supply or a service-life promise. The 70 Ω is not pentode plate resistance.

Tung-Sol, 1 November 1958, gives at 100 V plate, 100 V screen, −1 V control grid: plate current 9 mA, screen current 3.5 mA, transconductance 3.65 mA/V, approximate plate resistance 0.25 MΩ. At 250 V plate with the other two potentials unchanged: 9.2 mA, 3.3 mA, 3.6 mA/V, 1.5 MΩ. About −20 V grid reduces transconductance to 10 µA/V. The suppressor must connect to cathode at the socket.

Tung-Sol design-center limits are 300 V plate, 3 W plate dissipation, 0.6 W screen dissipation, 90 V heater-to-cathode; control grid must not be positive and its negative limit is 50 V. The 300 V screen-supply rating is not permission for 300 V on the screen grid itself: the sheet refers to a separate restriction for actual screen voltage. Maximum grid-to-plate capacitance is 0.0035 pF, input 4.5 pF, output 5.5 pF; shielded measurement uses external shield No.316 connected to pins 2 and 7.

B7G base, bottom-view 7CM: control grid 1, cathode 2, heater 3 and 4, plate 5, screen grid 6, suppressor and internal shield 7. Both sheets give maximum diameter 19.05 mm, height above pin seating plane 47.625 mm, overall length 53.975 mm. Pin 7 is not spare: the external cathode connection specified for typical operation must be respected. Documentation: Sylvania Engineering Data Service 6BJ6A Advance Data, 22 August 1958, with reference to JEDEC 2276, 8 September 1958; Tung-Sol 6BJ6/6BJ6A, tentative data and curves, 1 November 1958, four pages.