What is the 300B-XLS-EmissionLabs vacuum tube?

The 300B-XLS-EmissionLabs (300B-XLS EML) is a triode vacuum tube designed for power (set) applications. Enhanced dissipation 300B..

What is a 300B-XLS-EmissionLabs substitute or equivalent?

Direct equivalents to the 300B-XLS-EmissionLabs include 300B family — check bias and dissipation envelope before substitution; XLS is uprated and not a blind drop-in in every 300B circuit. 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 300B-XLS-EmissionLabs?

Amplification factor μ ≈ 4, transconductance gm ≈ 5.5 mA/V, plate resistance rp ≈ 700 Ω, max plate voltage 450 V, max plate dissipation 40 W, heater 5 V / 1.2 A.

Is the 300B-XLS-EmissionLabs still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 300B-XLS-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 300B-XLS-EmissionLabs sound like?

Enhanced dissipation 300B.. 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.

300B-XLS-EmissionLabs 300B-XLS EML Triode Vacuum Tube

Also known as 300B family — check bias and dissipation envelope before substitution · XLS is uprated and not a blind drop-in in every 300B circuit

High-power directly-heated triode for single-ended amplification

TriodeHeater 5 V · 1.2 AUX-4Emission Labs 2010

Plate dissipation: 40W
Max plate voltage: 450V
Transconductance: 5.5mA/V

300B-XLS-EmissionLabs

Characteristics

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

HeaterDirectly heated

Specifications of 300B-XLS-EmissionLabs — Heater
Heater voltageVh	5 V
Heater currentIh	1.2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 300B-XLS-EmissionLabs — Limiting values
Plate voltageVa max	450 V
Plate dissipationPa max	40 W

Mechanical

Specifications of 300B-XLS-EmissionLabs — Mechanical
Base	UX-4
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 300B-XLS-EmissionLabs — Small signal
Transconductance	5.5 mA/V
Plate resistance	700 Ω
Amplification factor	4

Capacitances

Specifications of 300B-XLS-EmissionLabs — Capacitances
Grid–cathode	8.5 pF
Grid–plate	15 pF
Plate–cathode	4.1 pF

Charactereditorial reading, not a measurement

Specifications of 300B-XLS-EmissionLabs — Character
Gain	4%
Power	100%
Drive	99%
Linearity	95%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	Va	Vg1 / Rk	Ia	gm	μ	Source
Class A, single-endedtriode connection · fixed bias	300 V	-61 V	60 mA	5.5 mA/V	5	read on the sheet JJ Electronic · non visible · transcript

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
Headphone output

Generic triode power (set) stage

Hi-Fi stereoHeadphone ampPA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Emission Labs design notes (EML-12B-20A-20B-30A) · external audit feedback

Manufacturer datasheets

2 manufacturer datasheets cross-checked for 300B-XLS EML2 verified

300B-XLS-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: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The 300B-XLS-EmissionLabs is a directly-heated triode from Emission Labs, introduced around 2010. It provides a gain factor (μ) of 4 with 700Ω plate resistance. Commonly used in power (set) applications. Enhanced dissipation 300B.

History

Introduced: 2010
Manufacturer: Emission Labs
Era: Modern

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