12EA6

The 12EA6 is a miniature sharp-cutoff pentode for car radios supplied directly from a 12 V automotive battery. General Electric presents it in July 1957 for intermediate-frequency amplifiers, while Tung-Sol in April 1959 also describes RF amplification. In both cases anode and screen receive low battery voltage. RCA’s October 1959 sheet confirms sharp-cutoff classification and six-cell-battery receiver service.

Heating is indirect at 12.6 V, but current depends on the document: General Electric 1957 gives 0.175 A, while Tung-Sol and RCA 1959 give approximately 0.19 A. RCA allows 10–15.9 V DC and recommends 11–14 V for life; General Electric and Tung-Sol caution that extremes are only briefly tolerable, reducing performance at low voltage and life at high voltage. The seven-pin miniature base is 7BK: first grid 1, third grid and internal shield 2, heater 3 and 4, anode 5, second grid 6 and cathode 7.

Tables agree on the typical class A1 point: 12.6 V anode and screen, third grid at zero, 10 MΩ bypassed first-grid resistor, 3.2 mA anode current and 1.4 mA screen current. Transconductance is 3800 µmho, or 3.8 mA/V, and plate resistance approximately 32000 Ω. Approximately −3.4 V first-grid voltage reduces anode current to 10 µA. This is a cutoff figure, not a bias to substitute automatically into the typical operating point.

Unshielded capacitances are first grid–anode maximum 0.04 pF, input 11 pF and output 4 pF. Limits are 16 V anode and screen and no positive DC first-grid voltage. RCA also gives 16 V peak heater to cathode in either polarity and maximum first-grid circuit resistance 12 MΩ, also found in General Electric. Tung-Sol instead lists 10 MΩ for first- and third-grid circuits. These differences remain attached to the respective sheets rather than being standardized.

General Electric curves show currents and transconductance changing with voltages at low anode supply. Photographs include boxes with the multiple marking 12EK6/12DZ6/12EA6: they attest those replacements’ commercial presentation, not identity of every type parameter. The Precision 660 tester table contains a specific 12EA6 row; those instrument settings concern tube testing and differ from radio operating conditions.