12AX7

Basing (pinout)

Bottom view — the socket as you see it from the wiring side. Hover, tap, or focus a pin to name it. Read from the datasheet basing diagram (how to read these →).

Datasheets

Primary manufacturer data, via public tube-data archives. The model below is fitted to the tabulated "average characteristics" in these sheets; the datasheet files themselves are linked, never rehosted.

Circuit Codex model

A CC0 ngspice model in the Koren form, fitted here to the published anchor — no parameters copied from other model collections. Methodology →

Anchor

Va=250 V, Vg=-2 V → Ia=1.2 mA, gm=1600 µmho, µ=100

Source

RCA Receiving Tube Manual RC-19, 1959, average characteristics

Note

Two-point fit (adopted 2026-07-18 from the calibration study below): the plate-current curve is held at both tabulated operating points — 250 V/−2 V and 100 V/−1 V — which all four manufacturers print identically. The low-plate-voltage behaviour of this tube was the subject of the 12AX7 calibration study.

File

models/12ax7.inc ↗

See these parameters drawn: the load line explorer plots the 12AX7's plate-curve family from this model and solves an operating point on it.

Maximum ratings

Design-centre values, each section. One watt is a small budget, but a 12AX7 gain stage idles at well under a milliamp — a 100 kΩ plate load and 1.5 kΩ cathode resistor put roughly 0.2 W into the plate, a fifth of the ceiling.

Plate voltage

300 V

Positive DC grid voltage

0 V

Negative DC grid voltage

50 V

Plate dissipation

1 W

Heater-cathode voltage

180 V either polarity

Rating system

Design centre — carries an allowance for manufacturing spread

Source

GE 12AX7 data sheet ET-T509B (June 1953), design-centre values, each section ↗

Related study