What is the 12AX7 vacuum tube?

The 12AX7 (12AX7 / ECC83) is a triode vacuum tube designed for preamp applications. Rich warm midrange. The gold standard..

What is a 12AX7 substitute or equivalent?

Direct equivalents to the 12AX7 include ECC83, 7025. These share the same pinout and operating envelope, so they can usually be swapped without circuit changes — though batch-to-batch variations between manufacturers (NOS vs current production) may shift the sonic character noticeably.

What are the key specifications of the 12AX7?

Amplification factor μ ≈ 100, transconductance gm ≈ 1.6 mA/V, plate resistance rp ≈ 62.5 kΩ, max plate voltage 300 V, max plate dissipation 1 W, heater 12.6 V / 0.15 A.

Is the 12AX7 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 12AX7 as Common availability. NOS (new-old-stock) examples from RCA, Mullard, Tung-Sol, GE, Sylvania and Telefunken trade among collectors; modern production where it exists comes mostly from JJ Electronic, Electro-Harmonix, Tung-Sol (New Sensor), Genalex, and a handful of small-batch makers.

What does the 12AX7 sound like?

Rich warm midrange. The gold standard.. Sonic character also depends heavily on the circuit operating point, the surrounding tubes in the stage, and the output transformer when present — use the interactive loadline calculator on this page to explore the trade-offs.

12AX7 ECC83 Triode Vacuum Tube

Also known as ECC83 · 7025

High-gain dual triode — the standard for guitar and hi-fi preamps

Dual triodeHeater 12.6 V · 0.15 A9-pin Noval2 sectionsMullard·RCA·Telefunken 1947

Plate dissipation: 1W
Max plate voltage: 300V
Amplification factor: 100
Transconductance: 1.6mA/V
Plate resistance: 62.5kΩ

12AX7

Characteristics

Datasheet values, once each. Every value cites its sheet.

HeaterIndirectly heated

Specifications of 12AX7 — Heater
Heater voltageVh	12.6 V
Heater currentIh	0.15 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 12AX7 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	1 W

Mechanical

Specifications of 12AX7 — Mechanical
Base	9-pin Noval
Rarity	Common
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 12AX7 — Small signal
Transconductance	1.6 mA/V
Plate resistance	62.5 kΩ
Amplification factor	100

Capacitances

Specifications of 12AX7 — Capacitances
Grid–cathode	1.6 pF
Grid–plate	1.7 pF
Plate–cathode	0.46 pF

Charactereditorial reading, not a measurement

Specifications of 12AX7 — Character
Gain	100%
Power	3%
Drive	38%
Linearity	50%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Typical operation

Canonical operating pointSPICE model4 availableModel

B+: 300 V
Load: 220 kΩ
Va: 180 V
Ia: 0.79 mA
Vg: -1.6 V
Pd: 0.14 W
Gain: 37.6 dB

At Q: Ayumi Nakabayashi · 4 engines
μ: 95.8
gm: 1.32 mA/V
rp: 72.4 kΩ

Design a stage →

Using this tube

Applications

Voltage amplifier
High-gain preamp
Phase splitter

Fender Tweed preampMarshall JTM45 V1Vox AC30 preampMarantz 7 phono stage

Guitar ampHi-Fi stereoHeadphone ampStudio/recording

Featured in these amplifiers

Classic circuits

12AX7 Guitar Preamp
Preamp Stage
Standard 12AX7 first gain stage as used in Fender, Marshall, and most guitar amplifiers. 100kΩ plate resistor with bypassed cathode.
SEVb 250V · Vg -1.5V · RL 100kΩFender/Marshall Guitar Amp Schematics
12AX7 Hi-Fi Preamp
Preamp Stage
12AX7 high-fidelity line stage with 220kΩ plate load. Higher supply voltage and larger plate resistor for maximum linearity and gain.
SEVb 300V · Vg -1.2V · RL 220kΩMarantz 7 Preamp Schematic

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Mullard·RCA·Telefunken datasheetActive model : Ayumi Nakabayashi · 4 engines

Manufacturer datasheets

4 manufacturer datasheets cross-checked for 12AX7 / ECC834 verified

12AX7 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Mullard·RCA·Telefunken datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 4 engines

Context

The 12AX7 (ECC83) is the most widely used small-signal dual triode in audio, with a voltage gain factor (mu) of 100 and medium plate resistance of approximately 62.5k ohms. It defines the preamp sound of virtually every guitar amplifier made since the 1950s and serves as the default first-stage gain tube in countless hi-fi phono stages and line preamps. Its high gain makes it ideal where maximum voltage amplification is needed, though its relatively high plate resistance limits its ability to drive low-impedance loads or long cable runs. Mullard, Telefunken, and RCA long-plate variants remain the most sought-after NOS examples, each with a distinct sonic fingerprint.

History

Introduced: 1947
Manufacturer: Mullard·RCA·Telefunken
Era: Golden Age

METRIX TESTER