What is the PP6/400 vacuum tube?

The PP6/400 is a triode vacuum tube designed for power (set) applications. British military variant..

What is a PP6/400 substitute or equivalent?

Direct equivalents to the PP6/400 include PP5/400. 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 PP6/400?

Amplification factor μ ≈ 9.5, transconductance gm ≈ 7.5 mA/V, plate resistance rp ≈ 1.3 kΩ, max plate voltage 400 V, max plate dissipation 25 W, heater 4 V / 1.5 A.

Is the PP6/400 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the PP6/400 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 PP6/400 sound like?

British military variant.. 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 10, 2026

←PP6/400

← PP5/400 PX25 →Compare → PP5/400

PP6/400 Triode Vacuum Tube

Triode4V / 1.5AUX-4SPICE

SourceMullard.org PX25/PP6-400 familyReviewed2026-05-10StatusDataModelCalcModelNorman KorenPDF

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

Datasheet ↗SPICE

PP6/400 — Osram — triode vacuum tube — (1935)

9.5

1.3kΩ

7.5mA/V

6.5pF

13.0pF

4.50pF

GAIN10%

POWER63%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater4 V · 1.5 A

Max Plate Voltage400 V

Pa max25 W

Gain Factor9.5

gm7.5 mA/V

rp1.3 kΩ

Inter-electrode capacitances

Cgk6.5 pF

Cgp13 pF

Cpk4.5 pF

PinoutUX-4

Era1935

RarityRare

HEATER4V / 1.5A

MAX PLATE400V / 25W

BASEux4

TYPICAL OPERATING POINT

Va350V

Ia53.64mA

Vg-26.573415V

Pd18.78W

RL3kΩ

Av15.8dB

EXECUTIVE SUMMARY

The PP6/400 is a directly-heated triode from Osram, introduced around 1935. It provides a gain factor (μ) of 9.5 with 1265Ω plate resistance. Commonly used in power (set) applications. British military variant.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

VS PP5/400

μ +6%Rp -16%Pd 0%Full comparison →

HISTORY

Introduced1935ManufacturerOsram

Pre-War