12AU6

12AU6 is also designated HF94. Completed sales put the typical price at $8.99 per tube.

Overview

The 12AU6 is a miniature pentode amplifier with a sharp cut-off control characteristic, using coated unipotential cathode construction. It is intended for service as an RF or AF amplifier and may be operated in any mounting position.

Construction

The tube uses a JEDEC 7BK base. Its heater is rated at 12.6 ± 1.3 volts, 150 mA AC or DC. The heater current has a maximum permissible deviation of ±6% from the nominal value of 150 mA.

Ratings

The Tung-Sol datasheet gives maximum ratings for the 12AU6 as follows: plate voltage 275 volts in pentode connection and 330 volts in triode connection; grid #2 supply voltage 330 volts; plate dissipation 3.5 watts; positive DC grid #1 voltage 0 volts; and heater-cathode voltage 200 volts with the heater either negative or positive with respect to the cathode. The Tung-Sol datasheet also gives grid-to-plate capacitance (G1 to P) as 0.0035 pF.

In pentode connection, typical operation is given at plate voltage 250 V, grid #2 voltage 150 V, and cathode bias resistor 68 ohms, yielding transconductance 5200 µmhos, plate current 10.6 mA, grid #2 current 4.3 mA, plate resistance 1.0 megohm, and grid #1 voltage -6.5 V for 10 mA plate current. In triode connection, with grid #2 connected to plate, cathode resistor 330 ohms, and grid #3 connected to plate, the transconductance is 4800 µmhos at 250 plate volts, with amplification factor 36 and plate current 12.2 mA.

Additional Notes

The Tung-Sol datasheet plate #3917 was issued August 1, 1954 by Tung-Sol Electric Inc., Electron Tube Division, Bloomfield, New Jersey. The German datasheet for the HF94, which corresponds to this type, provides further details: it states an oxide cathode, indirectly heated; weight approximately 8.5 g; recommends heater pin 2 be preferably grounded or at the lowest potential with respect to earth or chassis; and notes that the centre pin of the socket is used for decoupling grid 1 and anode and must be connected to earth or chassis. The German datasheet also gives maximum ratings including anode cold voltage 550 V, anode voltage 300 V, anode dissipation 3 W, screen-grid cold voltage 550 V, screen-grid voltage at 10.8 mA anode current 150 V, screen-grid dissipation 0.65 W, cathode current 20 mA, grid bias voltage range 0 to -50 V, grid-leak resistance 2 megohms, external resistance between heater and cathode 10 kΩ, and voltage between heater and cathode 100 V. It gives input capacitance as 5.5 pF, output capacitance as 5.0 pF, and grid 1 to anode capacitance as less than 0.0035 pF. It also states that, without special measures against hum or microphony, the HF94 may be used in a circuit where a voltage of 10 mV at grid 1 is required for 50 mW output in the output stage.

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, 2026-06-15 to 2026-11-01. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 12AU6, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• 3.Messwerte (statisch) (filed under HF94)
• TUNG-SOL -