12AJ7

The 12AJ7 is a nine-pin miniature triode–heptode described for frequency conversion and RF/IF amplification in transformerless AM/FM receivers. Triode and heptode share a cathode; the triode grid and heptode grid 3 are brought to pins 9 and 7 respectively. The heater requires 12.6 V, 0.15 A. The sheet also includes an application circuit linking the FM converter, 12AJ7 stage and following IF amplifier.

In the typical circuit, a 12DT8 precedes the 12AJ7 in the FM path, while the AM aerial circuit and AM oscillator coil connect to the 12AJ7. Switching changes the signal path and tuned-circuit connections; downstream is a 12BA6 with IF transformers and AGC. The sheet thus illustrates different receiver roles of the multigrid section, without assigning every FM-tuner function to the 12AJ7.

Converter data use anode 100 V, screen grids 2 and 4 at 63 V, control grid −1.1 V and oscillator grid resistor 47 kΩ. They give anode current 1.7 mA, combined grid-2/4 current 3.7 mA, grid-3-plus-triode-grid current 115 µA, conversion transconductance 620 µS and approximate anode resistance 800 kΩ. RF/IF amplifier data use anode 100 V, screens 60 V, grid 1 −1.1 V and grid 3 zero: anode current 3.4 mA, screen current 2.2 mA, transconductance 2 mA/V and approximate anode resistance 450 kΩ. Conversion transconductance must not be confused with amplifier transconductance.

Design-center maximums are anode 250 V and dissipation 0.8 W for the triode, 240 V and 1.7 W for the heptode. The table limits heptode grid-2 supply to 125 V and its dissipation to 1 W; maximum total cathode currents are triode 6.5 mA and heptode 12.5 mA. Peak heater–cathode limit is 100 V either polarity; grid-1 circuit resistance is at most 3 MΩ for either section. Without an external shield, grid–anode capacitance is 1 pF triode and at most 0.006 pF heptode; anode-to-anode capacitance is 0.2 pF.

Noval B9A base, E9-1: 1 heptode grids 2 and 4, 2 heptode grid 1, 3 common cathode with heptode grid 5 and internal shield, 4 and 5 heater, 6 heptode anode, 7 heptode grid 3, 8 triode anode, 9 triode grid. Any mounting position. Drawing maximums: overall length 2 5/8 inches, 66.675 mm, seated height 2 3/8 inches, 60.325 mm, diameter 7/8 inch, 22.225 mm; bulb excluding tip 2 ±3/32 inches, 50.8 ±2.38125 mm. Documentation: 12AJ7 Triode Heptode sheet, pages 239–240, with data and typical circuit.