What is the 6KX8 vacuum tube?

The 6KX8 is a triode vacuum tube designed for preamp applications. Compactron dual section..

What is a 6KX8 substitute or equivalent?

Direct equivalents to the 6KX8 include ECC808, 12AX7. 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 6KX8?

Amplification factor μ ≈ 100, transconductance gm ≈ 1.6 mA/V, plate resistance rp ≈ 62.5 kΩ, max plate voltage 300 V, max plate dissipation 1 W, heater 6.3 V / 0.34 A.

Is the 6KX8 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6KX8 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 6KX8 sound like?

Compactron dual section.. 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.

6KX8 Triode Vacuum Tube

Also known as ECC808 · 12AX7

High-gain dual triode — the standard for guitar and hi-fi preamps

Dual triodeHeater 6.3 V · 0.34 A9-pin Noval2 sectionsRCA 1962

Plate dissipation: 1W
Max plate voltage: 300V
Amplification factor: 100
Transconductance: 1.6mA/V
Plate resistance: 62.5kΩ

6KX8

Characteristics

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

HeaterIndirectly heated

Specifications of 6KX8 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.34 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6KX8 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	1 W

Mechanical

Specifications of 6KX8 — Mechanical
Base	9-pin Noval
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6KX8 — Small signal
Transconductance	1.6 mA/V
Plate resistance	62.5 kΩ
Amplification factor	100

Capacitances

Specifications of 6KX8 — Capacitances
Grid–cathode	2.5 pF
Grid–plate	1.3 pF
Plate–cathode	0.8 pF

Charactereditorial reading, not a measurement

Specifications of 6KX8 — Character
Gain	100%
Power	3%
Drive	38%
Linearity	50%

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

Typical operation

Canonical operating pointModel

B+: 250 V
Load: 125 kΩ
Va: 150 V
Ia: 1.08 mA
Vg: -1 V
Pd: 0.16 W
Gain: 36.9 dB

At Q: Norman Koren
μ: 106.4
gm: 1.61 mA/V
rp: 66 kΩ

Design a stage →

Using this tube

Applications

Voltage amplifier
High-gain preamp
Phase splitter

Generic triode preamp stage

Hi-Fi stereoHeadphone ampStudio/recording

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : amplifiedparts/r-type.org 6KX8/ECC808 dual triodeActive model : Norman Koren

Manufacturer datasheets

6KX8 DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: amplifiedparts/r-type.org 6KX8/ECC808 dual triode
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The 6KX8 is a dual indirectly-heated triode from RCA, introduced around 1962. It provides a gain factor (μ) of 100 with 62.5kΩ plate resistance. Commonly used in preamp applications. Compactron dual section.

History

Introduced: 1962
Manufacturer: RCA
Era: Late Production

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