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.

PX25 (Osram) Triode Vacuum Tube

Also known as DA60

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

TriodeHeater 4 V · 2 AUX-4Osram 1933

Plate dissipation: 25W
Max plate voltage: 400V
Transconductance: 8mA/V

PX25

Characteristics

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

HeaterDirectly heated

Specifications of PX25 — Heater
Heater voltageVh	4 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of PX25 — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	25 W

Mechanical

Specifications of PX25 — Mechanical
Base	UX-4
Rarity	Legendary
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of PX25 — Small signal
Transconductance	8 mA/V
Plate resistance	1.3 kΩ
Amplification factor	10

Capacitances

Specifications of PX25 — Capacitances
Grid–cathode	11.4 pF
Grid–plate	14.8 pF
Plate–cathode	8.3 pF

Charactereditorial reading, not a measurement

Specifications of PX25 — 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 (set) stage

Hi-Fi stereoHeadphone amp

Classic circuits

PX25 SE Classic
Single-Ended Triode6W
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 4kΩOsram PX25 Datasheet

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : TubeAmpDoctor PX25 datasheet · Mullard.org PX25/VR40 familyActive model : Norman Koren

Manufacturer datasheets

2 manufacturer datasheets cross-checked for PX25 (Osram)2 verified

PX25 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: TubeAmpDoctor PX25 datasheet · Mullard.org PX25/VR40 family
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

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.

History

Introduced: 1933
Manufacturer: Osram
Era: Pre-War

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