What is the 20B-EmissionLabs vacuum tube?

The 20B-EmissionLabs (20B EML) is a triode vacuum tube designed for power (set) applications. Enhanced 20A..

What is a 20B-EmissionLabs substitute or equivalent?

Direct equivalents to the 20B-EmissionLabs include 20A. 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 20B-EmissionLabs?

Amplification factor μ ≈ 21, transconductance gm ≈ 4.5 mA/V, plate resistance rp ≈ 4.7 kΩ, max plate voltage 600 V, max plate dissipation 25 W, heater 5 V / 2 A.

Is the 20B-EmissionLabs still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 20B-EmissionLabs as Sought-after 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 20B-EmissionLabs sound like?

Enhanced 20A.. 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 10, 2026

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20B-EmissionLabs 20B EML Triode Vacuum Tube

Triode5V / 2AUX-4

SourceEmission Labs design notes (EML-12B-20A-20B-30A) · external audit feedbackReviewed2026-05-10StatusDataModelCalcModelunder reviewPDF

Power triode delivering 25W for push-pull and SET designs

Datasheet ↗

20B EML — Emission Labs — triode vacuum tube — (2008)

4.7kΩ

4.5mA/V

9.0pF

15.0pF

7.00pF

GAIN21%

POWER63%

DRIVE95%

LINEARITY90%

SPECIFICATIONS

Heater5 V · 2 A

Max Plate Voltage600 V

Pa max25 W

Gain Factor21

gm4.5 mA/V

rp4.7 kΩ

Inter-electrode capacitances

Cgk9 pF

Cgp15 pF

Cpk7 pF

PinoutUX-4

Era2008

RaritySought-after

HEATER5V / 2A

MAX PLATE600V / 25W

BASEux4

EXECUTIVE SUMMARY

The 20B-EmissionLabs is a directly-heated triode from Emission Labs, introduced around 2008. It provides a gain factor (μ) of 21 with 4670Ω plate resistance. Commonly used in power (set) applications. Enhanced 20A.

APPLICATIONS

SET outputPush-pull output

Generic triode power (set) stage

• Hi-Fi stereo

HISTORY

Introduced2008ManufacturerEmission Labs

Modern

20B-EmissionLabs Datasheet

Frank's Electron Tube Pages · PDF

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METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

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