6AU4GTA

The 6AU4GTA is an indirectly heated vacuum rectifier diode designed as a damper in the horizontal-deflection circuit of television receivers. In that position it conducts during part of the line cycle and withstands the pulses produced by the circuit; it should not be treated as an ordinary mains rectifier. The General Electric sheet calls it particularly suitable for autotransformer deflection systems used with the 6CD6-GA. Compared with the 6AU4GT, the GTA designation chiefly marks higher permitted DC output and steady-state peak plate currents: Sylvania distinguishes 190 and 1150 mA for the GTA from 175 and 1050 mA for the GT.

The 6AU4GTA heater requires 6.3 V and 1.8 A on AC or DC. Several manufacturers state an average tube voltage drop of 25 V when the plate carries 350 mA DC: this is a test point, not a fixed drop at every current. The GE and Sylvania service ratings refer to a 525-line, 30-frame television system whose horizontal-voltage pulses occupy no more than 15% of a scanning cycle. Sylvania expressly advises against use as a power rectifier; the intended role remains recovery and damping in the line stage.

Limits from sheets using different rating systems must not be combined. The 4500 V peak inverse voltage is separately marked as an absolute maximum by GE, Sylvania and Tung-Sol; RCA gives the same number as a maximum in its sheet. The GTA design-center values in GE's 1955 and Sylvania's 1956 sheets are instead 190 mA DC current, 1150 mA steady-state peak current and 6.0 W plate dissipation. RCA and Tung-Sol sheets using design-maximum values state 210 mA, 1300 mA and 6.5 W. The larger figures do not license mixing the most favorable conditions from different documents: a particular set calls for the chosen manufacturer's sheet and its pulse conditions.

The envelope is T-9 and the base is a short intermediate-shell octal with external barriers, in five- or six-contact B5-85 and B6-60 versions. The 4CG diagram assigns the cathode to pin 3, plate to pin 5 and heater to pins 7 and 8; pin 2 is an internal connection that must not be used. Pin 1 may be absent from the five-pin base, and the sources do not treat it as a functional terminal. Socket contacts 1, 2, 4 and 6 must not be used as tie points. Dimensioned sheets also distinguish overall length, height above the seating plane and glass diameter: these are not interchangeable measurements. Sources: General Electric, 6AU4-GTA/19AU4-GTA, January 1955; Sylvania, Engineering Data Service 6AU4GT/6AU4GTA, March 1956; RCA, 6AU4-GTA, August 1959; Tung-Sol, 6AU4GTA.