6AU6A Pentode — Interactive Vacuum Tube Simulator

Warming up…

Plate current

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Screen current

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gm (mA/V)

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Plate diss.

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Screen diss.

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Cathode temp

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Heater · 6.3 V / 0.3 A

Plate voltage (B+) 250 V Screen grid G2 125 V Control grid G1 bias −1.0 V

Disconnect G3 (tetrode mode) Labels

Class-A Amplifier Stage

Plate V (q)

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Plate I (q)

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Voltage gain

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Supply B+ 250 V Input signal (1 kHz) 0.30 V pk Grid bias −2.2 V

Plate load RL

Plate Characteristic Curves

The tube's data-sheet fingerprint: plate current vs. plate voltage, one curve per control-grid bias (screen at 125 V). The dashed line is your circuit's load line; the dot is your Q-point. Tap a curve to re-bias the amplifier.

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Grid bias (shared with Circuit) −2.2 V

A Tiny Giant

The 6AU6A is a sharp-cutoff pentode — five electrodes in a thumb-sized glass "miniature" envelope. Released by RCA in 1946 (the "A" revision followed in the early 1950s), it became one of the most common small-signal amplifier tubes of the radio & TV era. If a 1950s television received a station, a 6AU6 probably helped amplify it.

Pentode (5 electrodes)7-pin B7A baseRF / IF amplifiergm 5,200 µmho

How It Works — 5 Ideas

Thermionic emission. A 6.3 V heater warms the coated cathode to ~800 °C. Electrons literally boil off the hot surface into the vacuum (the "Edison effect," 1883).
Space charge. With nowhere to go, boiled-off electrons hover as a negative cloud around the cathode — a ready reservoir of charge.
The valve (control grid, G1). A mesh near the cathode held slightly negative. A tiny voltage change here throttles a large electron flow — amplification. Negative enough (≈ −8 V) and flow stops completely: cutoff.
The accelerator (screen grid, G2). At +125 V it pulls electrons hard toward the plate; most shoot straight through its mesh. It also electrostatically shields G1 from the plate, slashing feedback capacitance to ~0.0035 pF — the secret to radio-frequency gain.
The bouncer (suppressor grid, G3). Electrons slamming into the plate knock loose "secondary" electrons. G3, at cathode potential, shoves them back — curing the distorted "kink" that plagued earlier tetrodes.

Timeline

1883

Edison notices current flowing through vacuum to a plate — the Edison effect.

1906–07

De Forest adds a control grid to Fleming's diode valve: the triode can amplify.

1926

The screen-grid tetrode tames grid-plate capacitance; Tellegen & Holst at Philips add a suppressor grid — the pentode is born.

Late 1930s

RCA introduces the compact 7-pin "miniature" base; tubes shrink from bananas to thumbs.

1946

RCA releases the 6AU6 — a sharp-cutoff pentode for RF/IF amplification in the coming television boom.

Early 1950s

6AU6A: controlled ~11-second heater warm-up and higher heater-cathode rating, so dozens of tubes could share one series heater string in transformerless TV sets.

1950s–60s

Found in nearly every TV and FM radio IF strip, plus oscilloscopes, instruments, early computers, and some guitar & hi-fi amps.

1965 →

Transistors take over. Production fades by the 1980s, but New-Old-Stock 6AU6s are still loved by hobbyists and amp builders.

Data Sheet Highlights

Envelope / base	T-5½ miniature glass, 7-pin (B7A)
Heater	6.3 V · 0.30 A (A-version: controlled 11 s warm-up)
Max plate voltage	300 V
Max screen (G2) voltage	150 V
Max plate dissipation	3 W
Max screen dissipation	0.65 W
Heater–cathode max	±200 V (improved in 6AU6A)
Typical operation	Plate 250 V · Screen 125 V · Grid −1 V
→ Plate / screen current	10.8 mA / 4.3 mA
Transconductance	5,200 µmho (5.2 mA/V)
Plate resistance	≈ 0.5 MΩ
Cutoff bias (approx.)	−8 V
Grid-to-plate capacitance	0.0035 pF max — why it excels at RF
Equivalents / cousins	EF94 (Europe) · 6BA6 (remote-cutoff) · 3AU6 / 4AU6 / 12AU6 (heater variants)

Pinout — B7A Base (bottom view)

Tap a pin. This is the view you'd see wiring a socket from underneath.

Tap a pin to learn its job…

Sharp vs. Remote Cutoff

The 6AU6 is sharp-cutoff: full gain until current stops abruptly — ideal for clean, linear amplification. Its sibling the 6BA6 is remote-cutoff (variable-µ): its grid winding pitch varies, so gain fades gradually with bias — perfect for AGC-controlled volume in radio tuners.

Try These Experiments

🔥 Turn the heater off — every other voltage becomes irrelevant. No heat, no electrons.
🕳️ Set plate voltage below screen voltage and watch the screen grid hog the current — and exceed its 0.65 W rating.
⚡ Enable tetrode mode, then sweep plate voltage 0→150 V to find the secondary-emission kink the suppressor grid was invented to cure.
🎚️ In Circuit, raise the input until the output clips — once at cutoff, once at the knee.
📈 In Curves, tap different bias curves and watch the Q-point slide along the load line.

Simulation uses a simplified physics model tuned to match the real 6AU6A data sheet at its classic operating point: 250 V plate / 125 V screen / −1 V grid → 10.8 mA plate current, 4.3 mA screen current, gm ≈ 5.2 mA/V, cutoff ≈ −8 V.