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.

20B-EmissionLabs 20B EML Triode Vacuum Tube

Also known as 20A

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

TriodeHeater 5 V · 2 AUX-4Emission Labs 2008

Plate dissipation: 25W
Max plate voltage: 600V
Transconductance: 4.5mA/V

20B-EmissionLabs

Characteristics

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

HeaterDirectly heated

Specifications of 20B-EmissionLabs — Heater
Heater voltageVh	5 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 20B-EmissionLabs — Limiting values
Plate voltageVa max	600 V
Plate dissipationPa max	25 W

Mechanical

Specifications of 20B-EmissionLabs — Mechanical
Base	UX-4
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 20B-EmissionLabs — Small signal
Transconductance	4.5 mA/V
Plate resistance	4.7 kΩ
Amplification factor	21

Capacitances

Specifications of 20B-EmissionLabs — Capacitances
Grid–cathode	9 pF
Grid–plate	15 pF
Plate–cathode	7 pF

Charactereditorial reading, not a measurement

Specifications of 20B-EmissionLabs — Character
Gain	21%
Power	63%
Drive	95%
Linearity	90%

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

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

SET output
Push-pull output

Generic triode power (set) stage

Hi-Fi stereo

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 10, 2026Source : Emission Labs design notes (EML-12B-20A-20B-30A) · external audit feedback

Manufacturer datasheets

20B-EmissionLabs DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Emission Labs design notes (EML-12B-20A-20B-30A) · external audit feedback
Reviewed: 2026-05-10
Status: DataModelCalc
Model: under review

Context

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.

History

Introduced: 2008
Manufacturer: Emission Labs
Era: Modern

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