What is the AZ4 vacuum tube?

The AZ4 is a rectifier vacuum tube designed for rectifier applications. European high-current rectifier. HiFi favorite..

What is a AZ4 substitute or equivalent?

Direct equivalents to the AZ4 include RGN2004, AZ12. 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.

Is the AZ4 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the AZ4 as Sought-after 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 AZ4 sound like?

European high-current rectifier. HiFi favorite.. 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

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AZ4 Rectifier Vacuum Tube

Rectifier4V / 2.2ASide Contact P8A

SourceTelefunken AZ4 datasheetReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Full-wave rectifier for vacuum tube power supply designs

Datasheet ↗

AZ4 — Philips·Telefunken — rectifier vacuum tube — (1937)

5.0pF

6.5pF

4.00pF

GAIN0%

POWER0%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater4 V · 2.2 A

Max Plate Voltage1000 V

Pa max—

Gain Factor—

gm—

rp—

Inter-electrode capacitances

Cgk5 pF

Cgp6.5 pF

Cpk4 pF

PinoutSide Contact P8A

Era1937

RaritySought-after

HEATER4V / 2.2A

MAX PLATE1000V

BASEp8a

Source datasheets

5 manufacturer datasheets cross-checked for AZ4

5 verified

EXECUTIVE SUMMARY

The AZ4 is a indirectly-heated rectifier from Philips·Telefunken, introduced around 1937. Commonly used in rectifier applications. European high-current rectifier. HiFi favorite.

APPLICATIONS

Power supply rectification

Generic rectifier rectifier stage

HISTORY

Introduced1937ManufacturerPhilips·Telefunken

Pre-War

AZ4 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

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