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.

By Jean-Michel Falligan Devergne · Reviewed May 9, 2026

←DO24

← DCC90 E130L →Compare → PX25

DO24 Triode Vacuum Tube

Triode4V / 2ASpecialSPICE

Sourcemullard.org DO24 (PX25 family) / EML PX25Reviewed2026-05-09StatusDataModelCalcModelNorman KorenPDF

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

Datasheet ↗SPICE

DO24 — Mullard — triode vacuum tube — (1935)

1.0kΩ

7.0mA/V

6.0pF

12.0pF

5.00pF

GAIN7%

POWER63%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater4 V · 2 A

Max Plate Voltage400 V

Pa max25 W

Gain Factor7

gm7 mA/V

rp1.0 kΩ

Inter-electrode capacitances

Cgk6 pF

Cgp12 pF

Cpk5 pF

PinoutSpecial

Era1935

RarityRare

HEATER4V / 2A

MAX PLATE400V / 25W

BASEspecial

TYPICAL OPERATING POINT

Va350V

Ia53.32mA

Vg-26.619999999999997V

Pd18.66W

RL2kΩ

Av15.1dB

EXECUTIVE SUMMARY

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.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

VS PX25

μ -30%Rp -21%Pd 0%Full comparison →

HISTORY

Introduced1935ManufacturerMullard

Pre-War