What is the PX25 vacuum tube?

The PX25 (PX25 (Osram)) is a triode vacuum tube designed for power (set) applications. British DHT aristocrat..

What is a PX25 substitute or equivalent?

Direct equivalents to the PX25 include DA60. 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 PX25?

Amplification factor μ ≈ 10, transconductance gm ≈ 8 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 PX25 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the PX25 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 PX25 sound like?

British DHT aristocrat.. 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 29, 2026

←PX25

← PP6/400 PX25-EmissionLabs →Compare…

PX25 PX25 (Osram) Triode Vacuum Tube

Triode4V / 2AUX-4SPICE

SourceTubeAmpDoctor PX25 datasheet · Mullard.org PX25/VR40 familyReviewed2026-05-29StatusDataModelCalcModelNorman KorenPDF

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

Datasheet ↗SPICE

PX25 (Osram) — Osram — triode vacuum tube — (1933)

1.3kΩ

8.0mA/V

11.4pF

14.8pF

8.30pF

GAIN10%

POWER63%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater4 V · 2 A

Max Plate Voltage400 V

Pa max25 W

Gain Factor10

gm8 mA/V

rp1.3 kΩ

Inter-electrode capacitances

Cgk11.4 pF

Cgp14.8 pF

Cpk8.3 pF

PinoutUX-4

Era1933

RarityLegendary

HEATER4V / 2A

MAX PLATE400V / 25W

BASEux4

Source datasheets

2 manufacturer datasheets cross-checked for PX25 (Osram)

2 verified

TYPICAL OPERATING POINT

Va400V

Ia51.96mA

Vg-70V

Pd20.78W

RL3kΩ

Av7.2dB

EXECUTIVE SUMMARY

The PX25 is a British directly-heated power triode developed by Marconi-Osram (GEC/MOV) in the 1930s, delivering about 6-8W in single-ended Class A. It combines the tonal refinement of a 2A3 with greater power and a distinctly British midrange character that is lush without being syrupy. The tube's relatively low mu (~3.8) and low plate resistance make it very easy to drive but demanding of the output transformer. Original GEC PX25s are among the rarest and most expensive NOS audio tubes; current production from KR Audio and EML provide modern alternatives.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1933ManufacturerOsram

Pre-War

PX25 Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

CLASSIC CIRCUITS

Single-Ended Triode

PX25 SE Classic

Marconi-Osram PX25 at its recommended operating point. The British rival to the 300B. Elegant, refined sound with a distinctly European character.

SEVb 400V · Vg -60V · RL 4kΩ

Osram PX25 Datasheet

SIMILAR TRIODES

View all →

01APreamp 100THTransmitting (SET)101DPower (SET)10YPower (SET)12AT7Driver 12AU7Line / Headphone 12AX7Preamp 12AY7Preamp