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.

6U8A Pentode Vacuum Tube

Also known as ECF82

Triode + PentodeHeater 6.3 V · 0.45 A9-pin Noval2 sectionsRCA 1955

Triode · Plate dissipation: 2.5W
Triode · Amplification factor: 40
Pentode · Plate dissipation: 3W
Pentode · Transconductance: 5mA/V

6U8A

Characteristics

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

HeaterIndirectly heated

Specifications of 6U8A — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.45 A

Mechanical

Specifications of 6U8A — Mechanical
Base	9-pin Noval
Rarity	Common
Pinout

TriodeTriode

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6U8A-T — Triode — Limiting values
Plate voltageVa max	330 V
Plate dissipationPa max	2.5 W

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6U8A-T — Triode — Small signal
Transconductance	7.5 mA/V
Plate resistance	5.4 kΩ
Amplification factor	40

Capacitances

Specifications of 6U8A-T — Triode — Capacitances
Grid–cathode	2.8 pF
Grid–plate	1.8 pF
Plate–cathode	1.5 pF

Charactereditorial reading, not a measurement

Specifications of 6U8A-T — Triode — Character
Gain	40%
Power	6%
Drive	95%
Linearity	80%

PentodePentode

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6U8A-P — Pentode — Limiting values
Plate voltageVa max	330 V
Plate dissipationPa max	3 W

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6U8A-P — Pentode — Small signal
Transconductance	5 mA/V
Plate resistance	200 kΩ

Capacitances

Specifications of 6U8A-P — Pentode — Capacitances
Input	5 pF
Grid–plate	0.015 pF
Output	2.6 pF

Charactereditorial reading, not a measurement

Specifications of 6U8A-P — Pentode — Character
Gain	0%
Power	8%
Drive	0%
Linearity	75%

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

Using this tube

Applications

Phase splitter

Generic pentode preamp stage

Replace or compare

Sources

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

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

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.

History

Introduced: 1955
Manufacturer: RCA
Era: Golden Age

METRIX TESTER

Characteristics

HeaterIndirectly heated

Mechanical

TriodeTriode

Limiting valuesDatasheet maximum ratings — not to be exceeded

Small signalDatasheet parameters at the reference operating point — not limits

Capacitances

Charactereditorial reading, not a measurement?

PentodePentode

Limiting valuesDatasheet maximum ratings — not to be exceeded

Small signalDatasheet parameters at the reference operating point — not limits

Capacitances

Charactereditorial reading, not a measurement?

Using this tube

Applications

Replace or compare

Versus 12SJ7

Similar tubes

Sources

Manufacturer datasheets

SPICE models

Context

History

Test this tube on a Metrix

Charactereditorial reading, not a measurement

Charactereditorial reading, not a measurement