What is the P27-500 vacuum tube?

The P27-500 (P27/500) is a triode vacuum tube designed for power (set) applications. Philips direct-heated..

What is a P27-500 substitute or equivalent?

Direct equivalents to the P27-500 include AD1. 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 P27-500?

Amplification factor μ ≈ 9, transconductance gm ≈ 7.5 mA/V, plate resistance rp ≈ 1.2 kΩ, max plate voltage 500 V, max plate dissipation 25 W, heater 4 V / 2 A.

Is the P27-500 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the P27-500 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 P27-500 sound like?

Philips direct-heated.. 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

←P27-500

← Nuvistor 7587 PCC88 →Compare → AD1

P27-500 P27/500 Triode Vacuum Tube

Triode4V / 2AUX-4SPICE

Sourceaudit-eu_b (CLEAN — matches canonical datasheet)Reviewed2026-05-29StatusDataModelCalcModelNorman KorenPDF

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

Datasheet ↗SPICE

P27/500 — Philips — triode vacuum tube — (1935)

1.2kΩ

7.5mA/V

8.5pF

16.0pF

5.00pF

GAIN9%

POWER63%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater4 V · 2 A

Max Plate Voltage500 V

Pa max25 W

Gain Factor9

gm7.5 mA/V

rp1.2 kΩ

Inter-electrode capacitances

Cgk8.5 pF

Cgp16 pF

Cpk5 pF

PinoutUX-4

Era1935

RarityRare

HEATER4V / 2A

MAX PLATE500V / 25W

BASEux4

Source datasheets

1 manufacturer datasheets cross-checked for P27/500

1 verified

TYPICAL OPERATING POINT

Va425V

Ia43.06mA

Vg-37.0256249V

Pd18.3W

RL3kΩ

Av15.3dB

EXECUTIVE SUMMARY

The P27-500 is a directly-heated triode from Philips, introduced around 1935. It provides a gain factor (μ) of 9 with 1200Ω plate resistance. Commonly used in power (set) applications. Philips direct-heated.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

VS AD1

μ +125%Rp +79%Pd +67%Full comparison →

HISTORY

Introduced1935ManufacturerPhilips

Pre-War

P27-500 Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

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