12AT7

12AT7 is also designated ECC81. Completed sales put the typical price at $23.19 per tube.

The 12AT7 is an indirectly heated twin triode, with two separate triode structures mounted side by side in a standard T6 1/2 bulb; only the heater connections are common between the two units.

## Construction

Each triode unit is a separate structure, and the two units have separate heaters but common heater pin connections. The heater has a centre tap, enabling use in both AC and AC/DC equipment. The tube is based with a B.V.A. Standard base type B9A (Noval). The getter is attached to the anode. Maximum physical dimensions are an overall length of 2-3/16 inches, a diameter of 7/8 inch, and a seated height of 1-15/16 inches.

## Ratings

The heater can be operated in series at 12.6 volts with a nominal current of 0.15 ampere, or in parallel at 6.3 volts with a nominal current of 0.3 ampere. The maximum heater-cathode potential (DC) is 250 volts. Maximum ratings include an anode voltage of 300 volts, an anode dissipation of 2.5 watts, a cathode current of 20 mA, a negative control grid voltage of 50 volts, and an average grid current of 1 mA.

## Characteristics

At an anode load of 100,000 ohms and a grid bias of -3 volts, the amplification factor (μ) is 37 and the anode impedance is 33,000 ohms.

## Applications

The Brimar datasheet states that the 12AT7 is designed to perform efficiently as a frequency changer in receivers for short or ultra-short waves. It is not suitable for frequency changer application when the signal frequency is of the same order as the intermediate frequency, as on medium or long waves with an IF of 465 Kc/s. Under optimum conversion conditions with a peak oscillator voltage of 4.5 volts, the equivalent noise resistance referred to the mixer grid is approximately 1000 ohms. Measurements taken as a mixer at 430 Mc/s indicate a noise factor of about 10 and a conversion gain of the order of 5 db; at 45 Mc/s a noise factor of the order of 8 is obtainable.

The 12AT7 may be used as an oscillator either single ended or in push-pull. Using lines for the tuned circuit, one 12AT7 with the two halves in push-pull will deliver about 2 watts output at 400 Mc/s; under single ended oscillator conditions, rather under half the push-pull power is developed.

As a grounded grid amplifier, the Brimar datasheet gives an input impedance of 180 ohms at Va 250 volts and Vg -2 volts, and 150 ohms at Va 180 volts and Vg -1 volt. At 40 Mc/s, the input impedance in a grounded grid single ended condition is approximately 40 kΩ. A single ended grounded grid amplifier using half a 12AT7 will give a gain of about 10 db at 200 Mc/s and about 6 db at 400 Mc/s; the noise factor in this service is of the order of 8 at 200 Mc/s. At 200 Mc/s, a typical gain in a cascode arrangement is 14 db with a noise factor of 7.

The 12AT7 may also be used as a resistance coupled amplifier.

Equivalence is asserted only where the archive's own literature states it directly, in at least 40 separate documents. Tubes that merely substitute in some circuits are not listed here.

Base B9A, viewed from below (the wiring side), pins numbered clockwise from the key. Hand-verified.

Per-tube prices from completed sales, 2022-08-29 to 2026-11-09. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 12AT7, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• BRIMAR
• Typical characteristics and operating conditions (filed under ECC81)

1 further designation appears alongside 12AT7 in the literature but below the evidence threshold used here, so it is not listed as equivalent.