What is the 6S4A vacuum tube?

The 6S4A is a triode vacuum tube designed for driver applications. US medium-mu single triode used as driver / compact power triode..

What is a 6S4A substitute or equivalent?

Direct equivalents to the 6S4A include None. 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 6S4A?

Amplification factor μ ≈ 16, transconductance gm ≈ 4.5 mA/V, plate resistance rp ≈ 3.7 kΩ, max plate voltage 550 V, max plate dissipation 8.5 W, heater 6.3 V / 0.6 A.

Is the 6S4A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6S4A 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 6S4A sound like?

US medium-mu single triode used as driver / compact power triode.. 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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6S4A Triode Vacuum Tube

Triode6.3V / 0.6A9-pin NovalSPICE

Sourceamplifiedparts.com 6S4A datasheet · vinylsavor 6S4A · wording corrected: US tube, not RussianReviewed2026-05-29StatusDataModelCalcModel2 enginesPDF

Medium-gain triode for driver and line stage applications

Datasheet ↗SPICE

6S4A — GE·RCA·Sylvania (US, NOT Russian) — triode vacuum tube — (1965)

3.7kΩ

4.5mA/V

4.2pF

2.4pF

0.60pF

GAIN16%

POWER21%

DRIVE96%

LINEARITY92%

SPECIFICATIONS

Heater6.3 V · 0.6 A

Max Plate Voltage550 V

Pa max8.5 W

Gain Factor16

gm4.5 mA/V

rp3.7 kΩ

Inter-electrode capacitances

Cgk4.2 pF

Cgp2.4 pF

Cpk0.6 pF

Pinout9-pin Noval

Era1965

RarityCommon

HEATER6.3V / 0.6A

MAX PLATE550V / 8.5W

BASEnoval

Source datasheets

4 manufacturer datasheets cross-checked for 6S4A

4 verified

TYPICAL OPERATING POINT

SPICE model(2 available)2 .subckt available ↓

Va425V

Ia18.86mA

Vg-21.258732V

Pd8.01W

RL8kΩ

Av21.3dB

EXECUTIVE SUMMARY

The 6S4A is a indirectly-heated triode from GE·RCA·Sylvania (US, NOT Russian), introduced around 1965. It provides a gain factor (μ) of 16 with 3700Ω plate resistance. Commonly used in driver applications. US medium-mu single triode used as driver / compact power triode.

APPLICATIONS

Push-pull output

Generic triode driver stage

HISTORY

Introduced1965ManufacturerGE·RCA·Sylvania (US, NOT Russian)

Late Production

6S4A Datasheet

Local mirror · PDF

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METRIX TESTER

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