What is the NR47 vacuum tube?

The NR47 is a triode vacuum tube designed for power applications. European DHT..

What is a NR47 substitute or equivalent?

Direct equivalents to the NR47 include PX25 class. 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 NR47?

Amplification factor μ ≈ 9.5, transconductance gm ≈ 7.5 mA/V, plate resistance rp ≈ 1.3 kΩ, max plate voltage 400 V, max plate dissipation 25 W, heater 4 V / 2 A.

Is the NR47 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the NR47 as Rare 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 NR47 sound like?

European DHT.. 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.

NR47 Triode Vacuum Tube

Also known as PX25 class

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

TriodeHeater 4 V · 2 AUX-4Various 1940

Plate dissipation: 25W
Max plate voltage: 400V
Transconductance: 7.5mA/V

NR47

Characteristics

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

HeaterDirectly heated

Specifications of NR47 — Heater
Heater voltageVh	4 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of NR47 — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	25 W

Mechanical

Specifications of NR47 — Mechanical
Base	UX-4
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of NR47 — Small signal
Transconductance	7.5 mA/V
Plate resistance	1.3 kΩ
Amplification factor	9.5

Capacitances

Specifications of NR47 — Capacitances
Grid–cathode	5 pF
Grid–plate	8 pF
Plate–cathode	4 pF

Charactereditorial reading, not a measurement

Specifications of NR47 — Character
Gain	10%
Power	63%
Drive	99%
Linearity	95%

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

Using this tube

Applications

SET output
Push-pull output
Headphone output

Generic triode power stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 10, 2026Source : Mullard.org PX25/NR47 familyActive model : Norman Koren

Manufacturer datasheets

NR47 DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Mullard.org PX25/NR47 family
Reviewed: 2026-05-10
Status: DataModelCalc
Model: Norman Koren

Context

The NR47 is a directly-heated triode from Various, introduced around 1940. It provides a gain factor (μ) of 9.5 with 1265Ω plate resistance. Commonly used in power applications. European DHT.

History

Introduced: 1940
Manufacturer: Various
Era: Pre-War

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