12AX4GTA

The 12AX4GTA is a half-wave vacuum rectifier intended for damper service in television sweep circuits. Sylvania describes this family for direct-drive deflection circuits and groups the 6AX4GT, 12AX4GT and 12AX4GTA: according to its sheet, the three types are identical apart from heater characteristics. The full designation therefore matters, particularly in sets with series-connected heaters.

The 12AX4GTA heater requires 12.6 V and 0.6 A. A feature of the GTA version is controlled heater warm-up, with an average time of 11 seconds under the specified test conditions. Sylvania links this to television sets with series heater strings. RCA also describes it as a TV damper diode with controlled warm-up. Data for related versions alone do not establish interchangeability: heater voltage, current and circuit behaviour must be checked.

For damper service Sylvania gives a maximum peak inverse voltage of 4,400 V, maximum plate dissipation of 4.8 W, maximum DC plate current of 125 mA and a 750 mA steady-state peak-current limit. Average tube drop is 32 V at the test current of 250 mA; it is not fixed under all conditions. The ratings refer to a 525-line, 30-frame television system with a voltage pulse no longer than 15% of one scanning cycle. Peak inverse voltage is not an ordinary continuous plate voltage. Sylvania shows a T-9 bulb and 4CG pin arrangement on an octal base: cathode on pin 3, plate on 5 and heater on 7 and 8; pins 1, 2, 4 and 6 must not be used as tie points. Documentary sources: Sylvania sheet for 6AX4GT, 12AX4GT and 12AX4GTA; RCA data for 12AX4GTA.