Full-wave rectifier on Noval base with 6.3V heater — similar TV rectifier service but different base and full-wave vs half-wave topology
Electrical Specifications
Rectifier
Peak Inverse VoltagePeak Inverse Voltage4,400V
Voltage Drop (typical)Tube Voltage Drop (at Ib=250 mA DC)32V
Peak Anode Current (surge)Peak Output Current750mA
Max DC Output Current (total, not per-anode)Max DC Output Current125mA
Heater
Notes
TDSL lists 12AX4GT as a different-rating variant, and 6AX4GTA as the 6.3V heater version.
The GTA and GTB suffixes indicate improved glass envelope designs with the same electrical ratings.
Half-wave damper diode — used to recover energy stored in the horizontal deflection yoke inductance and boost the B+ supply voltage.
Peak inverse voltage of 4400V handles the flyback pulse generated during horizontal retrace.
Peak output current of 750 mA; DC output current rating is 125 mA in boost rectifier service.
Heater-cathode voltage rating is critical in this application — cathode operates at high positive potential relative to chassis ground.
Tube voltage drop (Vdrop) of 32V at Ib=250 mA DC is explicitly stated under 'Typical Operating Conditions and Characteristics' in the Tung-Sol 12AX4GTB datasheet (December 1, 1960, Plate #6052).
Pin Layout — Octal
1No Connection
2Heater
3Plate
4
Socket-Compatible Tubes ⚠ Not electrically compatible