What is the DO24 vacuum tube?

The DO24 is a triode vacuum tube designed for power (set) applications. German transmitting DHT..

What is a DO24 substitute or equivalent?

Direct equivalents to the DO24 include PX25, CV1040, VR40. 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 DO24?

Amplification factor μ ≈ 7, transconductance gm ≈ 7 mA/V, plate resistance rp ≈ 1.0 kΩ, max plate voltage 400 V, max plate dissipation 25 W, heater 4 V / 2 A.

Is the DO24 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the DO24 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 DO24 sound like?

German transmitting 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.

DO24 Triode Vacuum Tube

Also known as PX25 · CV1040 · VR40 · NR47 · PP5 · 400

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

TriodeHeater 4 V · 2 ASpecialMullard 1935

Plate dissipation: 25W
Max plate voltage: 400V
Transconductance: 7mA/V

DO24

Characteristics

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

HeaterDirectly heated

Specifications of DO24 — Heater
Heater voltageVh	4 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of DO24 — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	25 W

Mechanical

Specifications of DO24 — Mechanical
Base	Special
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of DO24 — Small signal
Transconductance	7 mA/V
Plate resistance	1 kΩ
Amplification factor	7

Capacitances

Specifications of DO24 — Capacitances
Grid–cathode	6 pF
Grid–plate	12 pF
Plate–cathode	5 pF

Charactereditorial reading, not a measurement

Specifications of DO24 — Character
Gain	7%
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 (set) stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 9, 2026Source : mullard.org DO24 (PX25 family) / EML PX25Active model : Norman Koren

Manufacturer datasheets

DO24 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: mullard.org DO24 (PX25 family) / EML PX25
Reviewed: 2026-05-09
Status: DataModelCalc
Model: Norman Koren

Context

The DO24 is a directly-heated triode from Mullard, introduced around 1935. It provides a gain factor (μ) of 7 with 1000Ω plate resistance. Commonly used in power (set) applications. German transmitting DHT.

History

Introduced: 1935
Manufacturer: Mullard
Era: Pre-War

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