What is the 6U8A vacuum tube?

The 6U8A is a pentode vacuum tube designed for preamp applications.

What is a 6U8A substitute or equivalent?

Direct equivalents to the 6U8A include ECF82. 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.

Is the 6U8A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6U8A 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 6U8A sound like?

Sonic character depends 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

6U8A Pentode Vacuum Tube

Triode + Pentode6.3 V · 0.45 A9-pin Noval2 sectionsAlso known asECF82

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : audit-us_b (CLEAN — matches canonical datasheet)

6U8A

In brief

TriodeTriode

μ: 40
gm: 7.5 mA/V
rp: 5.4 kΩ
Pa: 2.5 W

PentodePentode

gm: 5 mA/V
rp: 200 kΩ
Pa: 3 W

The 6U8A-T is a indirectly-heated triode from RCA, introduced around 1955. It provides a gain factor (μ) of 40 with 5400Ω plate resistance. Commonly used in preamp applications. Triode section. The 6U8A-P is a indirectly-heated pentode from RCA, introduced around 1955. Commonly used in preamp applications. Pentode section.

Limits

Specifications of 6U8A
Specification	Value	Source
Heater
Heater voltage	6.3 V	Datasheet
Heater current	0.45 A	Datasheet

Specifications of 6U8A-T — Triode
Specification	Value	Source
LimitsDatasheet maximum ratings — not to be exceeded
Max Plate V	330 V	Datasheet
Pa max	2.5 W	Datasheet

Using this tube

Open the loadline calculator

APPLICATIONS

Phase splitter

Generic pentode preamp stage

Replace or compare

Sources

Manufacturer datasheets

Triode

3 manufacturer datasheets cross-checked for 6U8A — Triode3 verified

Pentode

3 manufacturer datasheets cross-checked for 6U8A — Pentode3 verified

6U8A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: audit-us_b (CLEAN — matches canonical datasheet)
Reviewed: 2026-05-29
Status: DataModelCalc
Model: SPICE model

Context

HISTORY

Introduced: 1955
Manufacturer: RCA
Era: Golden Age

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