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.

AZ4 Rectifier Vacuum Tube

Also known as RGN2004 · AZ12

Full-wave rectifier for vacuum tube power supply designs

RectifierHeater 4 V · 2.2 ASide Contact P8APhilips·Telefunken 1937

Max DC output current: 200mA
Max RMS input per anode: 500V

AZ4

Characteristics

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

HeaterIndirectly heated

Specifications of AZ4 — Heater
Heater voltageVh	4 V
Heater currentIh	2.2 A

Rectifier limitsDatasheet maximum ratings — not to be exceeded

Specifications of AZ4 — Rectifier limits
Max RMS input voltage per anode	500 V
Io max (DC output current)	200 mA
Max reservoir capacitor	60 µF
Min series resistance per anode	100 Ω

Mechanical

Specifications of AZ4 — Mechanical
Base	Side Contact P8A
Rarity	Sought-after
Pinout

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

Power supply rectification

Generic rectifier rectifier stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Telefunken AZ4 datasheet

Manufacturer datasheets

5 manufacturer datasheets cross-checked for AZ45 verified

AZ4 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Telefunken AZ4 datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

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

History

Introduced: 1937
Manufacturer: Philips·Telefunken
Era: Pre-War

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