What is the 2A3 vacuum tube?

The 2A3 is a triode vacuum tube designed for power (set) applications. Crystalline SE power..

What are the key specifications of the 2A3?

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 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 2A3 as Collector 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 sound like?

Crystalline SE power.. 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.

2A3 Triode Vacuum Tube

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

TriodeHeater 2.5 V · 2.5 AUX-4RCA·WE·Shuguang 1932

Plate dissipation: 15W
Max plate voltage: 300V
Transconductance: 5.25mA/V

2A3

Characteristics

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

HeaterDirectly heated

Specifications of 2A3 — Heater
Heater voltageVh	2.5 V
Heater currentIh	2.5 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 2A3 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	15 W

Mechanical

Specifications of 2A3 — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 2A3 — Small signal
Transconductance	5.25 mA/V
Plate resistance	800 Ω
Amplification factor	4

Capacitances

Specifications of 2A3 — Capacitances
Grid–cathode	7.5 pF
Grid–plate	16.5 pF
Plate–cathode	5.5 pF

Charactereditorial reading, not a measurement

Specifications of 2A3 — Character
Gain	4%
Power	38%
Drive	99%
Linearity	95%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	Va	Vg1 / Rk	Ia	Load	Pout	gm	μ	rp	Source
Class A, single-endedtriode connection · fixed bias	250 V	-45 V	60 mA	2.5 kΩ	3.5 W	5.25 mA/V	4.2	800 Ω	OCR, to be checked RCA · 1947 · p. 1 · transcript

SPICE model2 available

Model at this condition: Ayumi Nakabayashi · 2 engines Model
μ: 4
gm: 4.69 mA/V
rp: 855 Ω

Design a stage →

Using this tube

Applications

SET output
Push-pull output
Headphone output

Western Electric 86 amplifierCary CAD-2A3SE

Hi-Fi stereoHeadphone amp

Classic circuits

Audio Note Kit 1 / Ongaku Style
Hi-Fi Classic3.5W
Single-ended 2A3 in the Audio Note tradition. Direct-heated triode purity with simple signal path. Intimate, holographic sound.
SEVb 250V · Vg -45V · RL 2.5kΩAudio Note Kit 1 Design
2A3 SE Classic
Single-Ended Triode3.5W
Standard single-ended 2A3 operating point per RCA data. Direct-heated triode at its most pure. Sweet, intimate, and harmonically rich.
SEVb 250V · Vg -45V · RL 2.5kΩRCA 2A3 Datasheet
6B4G SE Classic
Single-Ended Triode3.5W
Octal-base equivalent of the 2A3. Same operating parameters with a more modern base. Practical alternative for SE triode designs.
SEVb 250V · Vg -45V · RL 2.5kΩRCA 6B4G Datasheet

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : RCA·WE·Shuguang datasheetActive model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

4 manufacturer datasheets cross-checked for 2A34 verified

2A3 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·WE·Shuguang datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The 2A3 is a directly-heated power triode introduced by RCA in 1930, delivering about 3.5W in single-ended Class A. It has a remarkably low plate resistance (~800 ohms) for a DHT, giving it excellent damping factor and tight bass response without feedback. The 2A3 occupies a sweet spot between the delicacy of the 45 and the authority of the 300B, with a midrange that many consider the most natural of any power tube. Single-plate versions (such as the RCA mono-plate and Sovtek 2A3) are generally preferred over the original dual-plate construction for lower distortion and better linearity.

History

Introduced: 1932
Manufacturer: RCA·WE·Shuguang
Era: Pre-War

METRIX TESTER

Characteristics

HeaterDirectly heated

Limiting valuesDatasheet maximum ratings — not to be exceeded

Mechanical

Small signalDatasheet parameters at the reference operating point — not limits

Capacitances

Charactereditorial reading, not a measurement?

Typical operation

Using this tube

Applications

Classic circuits

Audio Note Kit 1 / Ongaku Style

2A3 SE Classic

6B4G SE Classic

Replace or compare

Versus 300B

Comparisons

Similar tubes