What is the 2A3-40 JJ vacuum tube?

The 2A3-40 JJ is a triode vacuum tube designed for power (set) applications. Enhanced 2A3..

What is a 2A3-40 JJ substitute or equivalent?

Direct equivalents to the 2A3-40 JJ include 2A3. 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 2A3-40 JJ?

Amplification factor μ ≈ 4, transconductance gm ≈ 5.25 mA/V, plate resistance rp ≈ 800 Ω, max plate voltage 300 V, max plate dissipation 15 W, heater 2.5 V / 2.5 A.

Is the 2A3-40 JJ still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 2A3-40 JJ 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 2A3-40 JJ sound like?

Enhanced 2A3.. 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.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

←2A3-40 JJ

← 2A3 300B →Compare → 2A3

2A3-40 JJ Triode Vacuum Tube

Triode2.5V / 2.5AUX-4SPICE

SourceJJ Electronic 2A3-40 specReviewed2026-05-29StatusDataModelCalcModelNorman KorenPDF

High-power directly-heated triode for single-ended amplification

Datasheet ↗SPICE

2A3-40 JJ — JJ Electronic — triode vacuum tube — (2005)

800Ω

5.3mA/V

7.5pF

16.5pF

5.50pF

GAIN4%

POWER38%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater2.5 V · 2.5 A

Max Plate Voltage300 V

Pa max15 W

Gain Factor4

gm5.25 mA/V

rp800 Ω

Inter-electrode capacitances

Cgk7.5 pF

Cgp16.5 pF

Cpk5.5 pF

PinoutUX-4

Era2005

RarityCommon

HEATER2.5V / 2.5A

MAX PLATE300V / 15W

BASEux4

TYPICAL OPERATING POINT

Va250V

Ia39.9mA

Vg-48.717927499999995V

Pd9.98W

RL2kΩ

Av8.1dB

EXECUTIVE SUMMARY

The 2A3-40 JJ is a directly-heated triode from JJ Electronic, introduced around 2005. It provides a gain factor (μ) of 4 with 800Ω plate resistance. Commonly used in power (set) applications. Enhanced 2A3.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

VS 2A3

μ 0%Rp +0%Pd 0%Full comparison →

HISTORY

Introduced2005ManufacturerJJ Electronic

Modern