What is the 6AQ8 vacuum tube?

The 6AQ8 is a triode vacuum tube designed for preamp applications. Frame-grid. Sharp..

What is a 6AQ8 substitute or equivalent?

Direct equivalents to the 6AQ8 include ECC85. 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 6AQ8?

Amplification factor μ ≈ 57, transconductance gm ≈ 5.9 mA/V, plate resistance rp ≈ 9.7 kΩ, max plate voltage 300 V, max plate dissipation 2.5 W, heater 6.3 V / 0.435 A.

Is the 6AQ8 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6AQ8 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 6AQ8 sound like?

Frame-grid. Sharp.. 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.

6AQ8 Triode Vacuum Tube

Also known as ECC85

Medium-gain triode for driver and line stage applications

Dual triodeHeater 6.3 V · 0.435 A9-pin Noval2 sectionsPhilips 1958

Plate dissipation: 2.5W
Max plate voltage: 300V
Amplification factor: 57
Transconductance: 5.9mA/V
Plate resistance: 9.7kΩ

6AQ8

Characteristics

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

HeaterIndirectly heated

Specifications of 6AQ8 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.435 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6AQ8 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	2.5 W

Mechanical

Specifications of 6AQ8 — Mechanical
Base	9-pin Noval
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6AQ8 — Small signal
Transconductance	5.9 mA/V
Plate resistance	9.7 kΩ
Amplification factor	57

Capacitances

Specifications of 6AQ8 — Capacitances
Grid–cathode	3 pF
Grid–plate	1.5 pF
Plate–cathode	0.18 pF

Charactereditorial reading, not a measurement

Specifications of 6AQ8 — Character
Gain	57%
Power	6%
Drive	90%
Linearity	72%

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

Typical operation

Canonical operating pointSPICE model2 availableModel

B+: 250 V
Load: 19 kΩ
Va: 150 V
Ia: 3.8 mA
Vg: -2 V
Pd: 0.57 W
Gain: 32.7 dB

At Q: Ayumi Nakabayashi · 2 engines
μ: 52.3
gm: 4.29 mA/V
rp: 12.2 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 : Philips ECC85/6AQ8 datasheetActive model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

2 manufacturer datasheets cross-checked for 6AQ82 verified

6AQ8 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Philips ECC85/6AQ8 datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The 6AQ8 is a dual indirectly-heated triode from Philips, introduced around 1958. It provides a gain factor (μ) of 57 with 9700Ω plate resistance. Commonly used in preamp applications. Frame-grid. Sharp.

History

Introduced: 1958
Manufacturer: Philips
Era: Golden Age

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