12AG6

The 12AG6 is a miniature heptode primarily designed to combine oscillator and mixer functions in car radios. Tung-Sol explicitly describes anode and screen supplies obtained directly from a 12 V battery. Frequency conversion therefore operates at much lower voltages than many traditional radio converters. Grid 1 belongs to the oscillator system; grid 3 receives the signal to be converted; grids 2 and 4 are connected together as screens.

The heater requires 12.6 V, 0.15 A, AC or DC. The automotive note gives absolute limits 10.0 and 15.9 V, warning of reduced performance or life near the extremes. The typical converter point uses anode and screens 12.6 V, grid-3 supply 0 V, bypassed grid-3 resistor 2.2 MΩ and grid-1 resistor 20 kΩ. Approximate grid-1 AC voltage is 0.085 V RMS. Anode current is 0.55 mA, screen current 1.4 mA, grid-1 current 0.050 mA and conversion transconductance 300 µA/V.

The conversion figure has an important test qualification: the maker uses the RETMA 50-cycle conversion-transconductance test but reduces the grid-3 signal from 1.0 to 0.1 V peak-to-peak. This is a measurement condition, not a statement that the radio operates at a 50 Hz radio frequency. At approximately −2 V on grid 3, conversion transconductance falls to 10 µA/V. Curves show conversion and current changes with oscillator current and signal-grid voltage.

Separate non-oscillating oscillator characteristics use anode 12.6 V, screens connected to anode, grids 1 and 3 at 0 V: amplification factor 9, transconductance 3.4 mA/V, cathode current 4.2 mA. Grid 1 near −4 V reduces anode current to 10 µA. The ratings table headed design-center gives maximum anode and screen voltage 16 V, maximum positive DC grid-3 voltage 0 V, maximum DC grid-1 current 0.2 mA and maximum grid-3 resistance 2.2 MΩ. These figures remain distinct from converter and oscillating operation.

The seven-pin B7G miniature base shows from below: 1 grid 1, 2 cathode, 3 and 4 heater, 5 anode, 6 grids 2 and 4, 7 grid 3. Any mounting position is allowed. Maximum diameter 3/4 inch (19.05 mm), maximum seated height 1 7/8 inches (47.625 mm), maximum overall height 2 1/8 inches (53.975 mm). Unshielded capacitances include grid 1–cathode 2.8 pF and maxima grid 3–anode 0.28 pF, grid 1–grid 3 of 0.17 pF, grid 1–anode 0.065 pF. Documentation: Tung-Sol, 12AG6, Heptode, Tentative Data, April 1, 1956, four pages with data and curves.