What is the PP5/400 vacuum tube?

The PP5/400 is a triode vacuum tube designed for power (set) applications. British military..

What is a PP5/400 substitute or equivalent?

Direct equivalents to the PP5/400 include PX4. 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 PP5/400?

Amplification factor μ ≈ 9, transconductance gm ≈ 6 mA/V, plate resistance rp ≈ 1.5 kΩ, max plate voltage 400 V, max plate dissipation 25 W, heater 4 V / 2 A.

Is the PP5/400 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the PP5/400 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 PP5/400 sound like?

British military.. 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.

PP5/400 Triode Vacuum Tube

Also known as PX4

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

TriodeHeater 4 V · 2 AUX-4Osram 1935

Plate dissipation: 25W
Max plate voltage: 400V
Transconductance: 6mA/V

PP5/400

Characteristics

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

HeaterDirectly heated

Specifications of PP5/400 — Heater
Heater voltageVh	4 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of PP5/400 — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	25 W

Mechanical

Specifications of PP5/400 — Mechanical
Base	UX-4
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of PP5/400 — Small signal
Transconductance	6 mA/V
Plate resistance	1.5 kΩ
Amplification factor	9

Capacitances

Specifications of PP5/400 — Capacitances
Grid–cathode	6 pF
Grid–plate	12 pF
Plate–cathode	4 pF

Charactereditorial reading, not a measurement

Specifications of PP5/400 — Character
Gain	9%
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 29, 2026Source : Mullard.org PX25/PP5-400 familyActive model : Norman Koren

Manufacturer datasheets

PP5/400 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Mullard.org PX25/PP5-400 family
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The PP5/400 is a directly-heated triode from Osram, introduced around 1935. It provides a gain factor (μ) of 9 with 1500Ω plate resistance. Commonly used in power (set) applications. British military.

History

Introduced: 1935
Manufacturer: Osram
Era: Pre-War

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