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.

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

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12B4A Triode Vacuum Tube

Triode12.6V / 0.3A9-pin NovalSPICE

SourceGE·RCAReviewed2026-05-29StatusDataModelCalcModelAyumi NakabayashiPDF

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

Datasheet ↗SPICE

12B4A — GE·RCA — triode vacuum tube — (1955)

1.0kΩ

6.3mA/V

5.0pF

4.8pF

1.50pF

GAIN6%

POWER14%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater12.6 V · 0.3 A

Max Plate Voltage550 V

Pa max5.5 W

Gain Factor6

gm6.3 mA/V

rp1.0 kΩ

Inter-electrode capacitances

Cgk5 pF

Cgp4.8 pF

Cpk1.5 pF

Pinout9-pin Noval

Era1955

RarityModerate

HEATER12.6V / 0.3A

MAX PLATE550V / 5.5W

BASEnoval

Source datasheets

3 manufacturer datasheets cross-checked for 12B4A

3 verified

TYPICAL OPERATING POINT

Va425V

Ia10.69mA

Vg-70.73843073V

Pd4.54W

RL2kΩ

Av8.4dB

EXECUTIVE SUMMARY

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.

APPLICATIONS

Push-pull outputHeadphone output

Generic triode line / headphone stage

• Headphone amp

HISTORY

Introduced1955ManufacturerGE·RCA

Golden Age

12B4A Datasheet

Local mirror · PDF

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METRIX TESTER

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