What is the 300B vacuum tube?

The 300B is a triode vacuum tube designed for power (set) applications. Holy grail of SET..

What is a 300B substitute or equivalent?

Direct equivalents to the 300B include Takatsuki, EML. 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?

Amplification factor μ ≈ 4, transconductance gm ≈ 5.5 mA/V, plate resistance rp ≈ 700 Ω, max plate voltage 400 V, max plate dissipation 36 W, heater 5 V / 1.2 A.

Is the 300B still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 300B as Legendary 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 sound like?

Holy grail of SET.. 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 Triode Vacuum Tube

Also known as Takatsuki · EML

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

TriodeHeater 5 V · 1.2 AUX-4Western Electric 1938

Plate dissipation: 36W
Max plate voltage: 400V
Transconductance: 5.5mA/V

300B

Characteristics

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

HeaterDirectly heated

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

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 300B — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	36 W

Mechanical

Specifications of 300B — Mechanical
Base	UX-4
Rarity	Legendary
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

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

Capacitances

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

Charactereditorial reading, not a measurement

Specifications of 300B — Character
Gain	4%
Power	90%
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	Load	Pout	THD	gm	μ	rp	Source
Class A, single-endedtriode connection · fixed bias	300 V	-61 V	62 mA	3 kΩ	6 W	5%	5.3 mA/V	3.9	740 Ω	OCR, to be checked Western Electric · 1950 · p. 2 · transcript
Class A, push-pulltriode connection · fixed bias · values for two tubes	300 V	-61 V	100 mA	4 kΩ a-a	10 W	4.5%				OCR, to be checked Western Electric · 1950 · p. 2 · transcript

SPICE model2 available

Model at this condition: Ayumi Nakabayashi · 2 engines Model
μ: 3.8
gm: 5.11 mA/V
rp: 750 Ω

Design a stage →

Using this tube

Applications

SET output
Push-pull output
Headphone output

Western Electric 91ACary CAD-300SEIAudio Note Kegon

Hi-Fi stereoHeadphone ampPA/public address

Classic circuits

Audio Note Kit 2 / 300B SE
Hi-Fi Classic8W
Single-ended 300B in the Kondo/Audio Note philosophy. Rich, detailed, and deeply three-dimensional sound. The SET reference.
SEVb 400V · Vg -70V · RL 3.5kΩAudio Note Kit 2 Design
300B SE Classic
Single-Ended Triode7W
Western Electric 300B at standard operating point. The most revered SET tube. Full-bodied, liquid midrange with natural dynamics.
SEVb 350V · Vg -61V · RL 3.5kΩWestern Electric 300B Datasheet

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Western Electric datasheetActive model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

2 manufacturer datasheets cross-checked for 300B2 verified

300B DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Western Electric datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The 300B is Western Electric's legendary directly-heated power triode, originally designed in 1938 for telephone repeater amplifiers and theater sound systems. It produces 8-10W in single-ended Class A with a linear, low-distortion transfer characteristic that has made it the reference standard for SET amplifiers. The tube's mu of 3.85 and plate resistance around 700 ohms yield a combination of authority and finesse that few power tubes match. Original WE 300Bs command collector prices, but current production from WE (reissue), Takatsuki, Elrog, and EML offer legitimate alternatives with varying sonic signatures.

History

Introduced: 1938
Manufacturer: Western Electric
Era: Pre-War

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