6J6A

The 6J6A is a miniature medium-mu twin triode with a cathode shared by both sections. RCA documentation describes its use as an RF power amplifier, oscillator and twin audio amplifier. Tung-Sol also describes parallel or push-pull operation: with push-pull grids and parallel plates, the type is intended for frequency conversion up to 600 MHz. This mixer arrangement is one of the valve's distinctive documented high-frequency applications.

The heater requires 6.3 V at 0.45 A, AC or DC. Construction uses a seven-pin miniature B7G base: plates are on pins 1 and 2, grids on 6 and 5 respectively, the common cathode on 7 and heater on 3 and 4. The shared cathode must be considered when reconstructing connections to both sections. Unshielded grid-to-plate capacitance is approximately 1.6 pF per triode; the RCA sheet also gives capacitances with an external shield connected to the cathode.

In the Tung-Sol sheet the A suffix identifies the version with controlled heater thermal characteristics, intended to limit warm-up voltage surges when used with other similarly controlled types. The stated time is about 11 seconds under the manufacturer's specified test: reaching 80% of rated voltage in a particular supply arrangement with a series resistor. The RCA manual also covers the 5J6, described as identical except for its 4.7 V, 0.6 A heater. These details call for attention to the heater chain when servicing equipment.

For class A, RCA specifies a 100 V plate supply and a common 50 Ω cathode resistor with both sections operating under the stated conditions. Each triode then has 8.5 mA plate current, amplification factor 38, approximately 7.1 kΩ plate resistance and 5.3 mA/V transconductance. The HB3 sheet sets design-center limits of 300 V plate voltage and 1.5 W dissipation for each section; peak heater-to-cathode voltage is 100 V in either direction. Maximum grid-circuit resistance for cathode bias is 0.5 MΩ; the manufacturer advises against fixed bias for this amplifier service.

RCA also gives an unmodulated class-C telegraphy example with both sections in push-pull up to 50 MHz: 150 V plate voltage, −10 V grid bias, 30 mA total plate current, about 0.35 W drive and approximately 3.5 W useful output. A separate note describes about 1 W as a push-pull oscillator at 250 MHz, with 150 V plate voltage, maximum rated dissipation and a common 2 kΩ grid resistor. Published curves supplement these examples by showing parameter changes with bias and plate voltage. Sources: RCA and Tung-Sol 6J6A sheets; RCA Receiving Tube Manual, 6J6A entry.