What is the VR40 vacuum tube?

The VR40 is a triode vacuum tube designed for power applications. Military PX25 variant..

What is a VR40 substitute or equivalent?

Direct equivalents to the VR40 include PX25. 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 VR40?

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 VR40 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the VR40 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 VR40 sound like?

Military PX25 variant.. 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.

VR40 Triode Vacuum Tube

Also known as PX25

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

TriodeHeater 4 V · 2 AUX-4Osram 1940

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

VR40

Characteristics

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

HeaterDirectly heated

Specifications of VR40 — Heater
Heater voltageVh	4 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of VR40 — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	25 W

Mechanical

Specifications of VR40 — Mechanical
Base	UX-4
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of VR40 — Small signal
Transconductance	7.5 mA/V
Plate resistance	1.3 kΩ
Amplification factor	9.5

Capacitances

Specifications of VR40 — Capacitances
Grid–cathode	5.5 pF
Grid–plate	9 pF
Plate–cathode	4.5 pF

Charactereditorial reading, not a measurement

Specifications of VR40 — 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/VR40 datasheetActive model : Norman Koren

Manufacturer datasheets

VR40 DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Mullard.org PX25/VR40 datasheet
Reviewed: 2026-05-10
Status: DataModelCalc
Model: Norman Koren

Context

The VR40 is a directly-heated triode from Osram, introduced around 1940. It provides a gain factor (μ) of 9.5 with 1265Ω plate resistance. Commonly used in power applications. Military PX25 variant.

History

Introduced: 1940
Manufacturer: Osram
Era: Pre-War

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