What is the 12B4A vacuum tube?

The 12B4A is a triode vacuum tube designed for line / headphone applications. Low mu single triode. 2A3 grandchild. OTL gem..

What is a 12B4A substitute or equivalent?

Direct equivalents to the 12B4A include 12B4. 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 12B4A?

Amplification factor μ ≈ 6, transconductance gm ≈ 6.3 mA/V, plate resistance rp ≈ 1.0 kΩ, max plate voltage 550 V, max plate dissipation 5.5 W, heater 12.6 V / 0.3 A.

Is the 12B4A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 12B4A as Moderate 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 12B4A sound like?

Low mu single triode. 2A3 grandchild. OTL gem.. 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.

12B4A Triode Vacuum Tube

Also known as 12B4

Low-mu triode with excellent linearity for driver and line stages

TriodeHeater 12.6 V · 0.3 A9-pin NovalGE·RCA 1955

Plate dissipation: 5.5W
Max plate voltage: 550V
Transconductance: 6.3mA/V

12B4A

Characteristics

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

HeaterIndirectly heated

Specifications of 12B4A — Heater
Heater voltageVh	12.6 V
Heater currentIh	0.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 12B4A — Limiting values
Plate voltageVa max	550 V
Plate dissipationPa max	5.5 W

Mechanical

Specifications of 12B4A — Mechanical
Base	9-pin Noval
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 12B4A — Small signal
Transconductance	6.3 mA/V
Plate resistance	1 kΩ
Amplification factor	6

Capacitances

Specifications of 12B4A — Capacitances
Grid–cathode	5 pF
Grid–plate	4.8 pF
Plate–cathode	1.5 pF

Charactereditorial reading, not a measurement

Specifications of 12B4A — Character
Gain	6%
Power	14%
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	gm	μ	Source
Class A, single-endedtriode connection · fixed bias	150 V	-17.5 V	34 mA	6.3 mA/V	6.5	OCR, to be checked RCA · 1955 · p. 1 · transcript

Model at this condition: Ayumi Nakabayashi Model
μ: 6.4
gm: 7.06 mA/V
rp: 900 Ω

Using this tube

Applications

Push-pull output
Headphone output

Generic triode line / headphone stage

Headphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Active model : Ayumi Nakabayashi

Manufacturer datasheets

3 manufacturer datasheets cross-checked for 12B4A3 verified

12B4A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: GE·RCA
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi

Context

The 12B4A is a indirectly-heated triode from GE·RCA, introduced around 1955. It provides a gain factor (μ) of 6 with 1030Ω plate resistance. Commonly used in line / headphone applications. Low mu single triode. 2A3 grandchild. OTL gem.

History

Introduced: 1955
Manufacturer: GE·RCA
Era: Golden Age

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