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 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.

6S4A Triode Vacuum Tube

Medium-gain triode for driver and line stage applications

TriodeHeater 6.3 V · 0.6 A9-pin NovalGE·RCA·Sylvania (US, NOT Russian) 1965

Plate dissipation: 8.5W
Max plate voltage: 550V
Transconductance: 4.5mA/V

6S4A

Characteristics

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

HeaterIndirectly heated

Specifications of 6S4A — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.6 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6S4A — Limiting values
Plate voltageVa max	550 V
Plate dissipationPa max	8.5 W

Mechanical

Specifications of 6S4A — Mechanical
Base	9-pin Noval
Rarity	Common
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6S4A — Small signal
Transconductance	4.5 mA/V
Plate resistance	3.7 kΩ
Amplification factor	16

Capacitances

Specifications of 6S4A — Capacitances
Grid–cathode	4.2 pF
Grid–plate	2.4 pF
Plate–cathode	0.6 pF

Charactereditorial reading, not a measurement

Specifications of 6S4A — Character
Gain	16%
Power	21%
Drive	96%
Linearity	92%

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	rp	Source
Class A, single-endedtriode connection · fixed bias	250 V	-8 V	24 mA	4.5 mA/V	16.5	3.7 kΩ	OCR, to be checked RCA · 1-62 (DATA 1) · p. 1 · transcript
triode connection, single-endedclass not stated · fixed bias	250 V	-8 V	24 mA	4.5 mA/V	16.5	3.7 kΩ	OCR, to be checked Tung-Sol Electric Inc. · 1962 · p. 2 · transcript

SPICE model2 available

Model at this condition: Ayumi Nakabayashi · 2 engines Model
μ: 16
gm: 4.65 mA/V
rp: 3.4 kΩ

Using this tube

Applications

Push-pull output

Generic triode driver stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : amplifiedparts.com 6S4A datasheet · vinylsavor 6S4A · wording corrected: US tube, not RussianActive model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

4 manufacturer datasheets cross-checked for 6S4A4 verified

6S4A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: amplifiedparts.com 6S4A datasheet · vinylsavor 6S4A · wording corrected: US tube, not Russian
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

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.

History

Introduced: 1965
Manufacturer: GE·RCA·Sylvania (US, NOT Russian)
Era: Late Production

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