6AC7

6AC7 is also designated 1852. Completed sales put the typical price at $7.97 per tube.

Description

The 6AC7 is a sharp-cutoff high-transconductance pentode intended for service as a wide-band video or radio-frequency amplifier. It is also suitable for use as a mixer or oscillator. The tube has a coated unipotential cathode and an MT-8 metal-shell envelope. Its heater is designed to operate on either a.c. or d.c. at a voltage of 6.3 volts and a current of 0.45 ampere.

Construction and Base

The electrode assembly is the same as that in the 1851, but a special shielded lead construction permits bringing out the control-grid lead to a base pin rather than to a pin cap. The proximity of the grid pin to the cathode pin simplifies wiring and decreases the size of the inductance loop connecting the input circuit to the tube. The base has pin 1 connected to the shell and internal shield, pin 2 to the heater, pin 3 to grid number 3 (suppressor), pin 4 to grid number 1, pin 5 to the cathode, pin 6 to grid number 2 (screen), pin 7 to the heater, and pin 8 to the plate.

Ratings and Characteristics

Maximum ratings include a plate voltage of 300 volts, a screen supply voltage of 300 volts, a screen voltage of 150 volts, a plate dissipation of 3.0 watts, a screen dissipation of 0.38 watt, and a heater-cathode voltage of 90 volts. The maximum grid circuit resistance is 0.25 megohm with fixed screen voltage and 0.5 megohm with a series screen resistor. Typical operating characteristics include a plate resistance of approximately 1.0 megohm, a transconductance of 9000 micromhos, a plate current of 10 milliamperes, and a screen current of 2.5 milliamperes. The maximum grid-to-plate capacitance is 0.015 micromicrofarads. The heater voltage should not deviate more than plus or minus 10% from the normal value of 6.3 volts.

Operating Notes

The datasheet recommends the use of cathode-bias. When a fixed screen voltage is used, a sharp-cutoff characteristic is obtained; when a screen resistor is used, an extended-cutoff characteristic is obtained. For applications where bias adjustment is used to vary gain, an extended cut-off characteristic may be obtained as shown in Condition II of the datasheet. The screen voltage in Condition I may be obtained from a potentiometer or bleeder circuit across the B-supply source. In video stages, the cathode-bias resistor should not be bypassed if degeneration and freedom from distortion are desired; when no degeneration and maximum amplitude are desired, the cathode-bias resistor should be by-passed with a large condenser (350 µf). The suppressor should be connected directly to ground in r-f and i-f stages to minimize feedback. The mounting position is any.

The potential difference between heater and cathode should be kept as low as possible. When operated from a transformer, the cathode should be connected through a bias resistor either to one side or to the electrical mid-point of the heater circuit. In the case of d-c operation from a 6-volt storage battery, the cathode circuit should be tied through a bias resistor to the negative battery terminal. The tube is not recommended for low-level audio-frequency applications unless the heater voltage is obtained from a d-c source.

Applications

The 6AC7 is intended for use by the amateur and experimenter in experimental television receivers. It is recommended for use in the r-f and i-f stages of the picture amplifier of such receivers, and may also be used in the first stages of the video amplifier when several video stages are employed. The tube can also be used as a mixer and makes a good oscillator in low-voltage applications.

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.

Per-tube prices from completed sales, 2026-08-04 to 2026-09-19. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 6AC7, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• Television Amplifier Pentode (filed under 1852)
• **Description and Rating**

1 further designation appears alongside 6AC7 in the literature but below the evidence threshold used here, so it is not listed as equivalent.