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.

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

←6KX8

← 6KD6 6L6G →Compare → ECC808

6KX8 Triode Vacuum Tube

Dual triode6.3V / 0.34A9-pin NovalSPICE

Sourceamplifiedparts/r-type.org 6KX8/ECC808 dual triodeReviewed2026-05-29StatusDataModelCalcModelNorman KorenPDF

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

Datasheet ↗SPICE

6KX8 — RCA — triode vacuum tube — (1962)

100

62.5kΩ

1.6mA/V

2.5pF

1.3pF

0.80pF

GAIN100%

POWER3%

DRIVE38%

LINEARITY50%

SPECIFICATIONS

Heater6.3 V · 0.34 A

Max Plate Voltage300 V

Pa max1 W

Gain Factor100

gm1.6 mA/V

rp62.5 kΩ

Inter-electrode capacitances

Cgk2.5 pF

Cgp1.3 pF

Cpk0.8 pF

Pinout9-pin Noval

Era1962

RarityModerate

HEATER6.3V / 0.34A

MAX PLATE300V / 1W

BASEnoval

SECTIONS2 (dual)

TYPICAL OPERATING POINT

Va150V

Ia1.08mA

Vg-1V

Pd0.16W

RL125kΩ

Av36.9dB

EXECUTIVE SUMMARY

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.

APPLICATIONS

Voltage amplifierHigh-gain preampPhase splitter

Generic triode preamp stage

• Hi-Fi stereo• Headphone amp• Studio/recording

VS ECC808

μ 0%Rp +0%Pd +100%Full comparison →

HISTORY

Introduced1962ManufacturerRCA

Late Production