What is the AD1 vacuum tube?

The AD1 is a triode vacuum tube designed for power (se) applications. Legendary European DHT. Queen of triodes..

What is a AD1 substitute or equivalent?

Direct equivalents to the AD1 include AD1/350, TAD1, RE604. 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 AD1?

Amplification factor μ ≈ 4, transconductance gm ≈ 6 mA/V, plate resistance rp ≈ 670 Ω, max plate voltage 250 V, max plate dissipation 15 W, heater 4 V / 0.95 A.

Is the AD1 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the AD1 as Legendary 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 AD1 sound like?

Legendary European DHT. Queen of triodes.. 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.

AD1 Triode Vacuum Tube

Also known as AD1 · 350 · TAD1 · RE604 · P15 · 250

High-power directly-heated triode for single-ended amplification

TriodeHeater 4 V · 0.95 AP8A side-contactPhilips·Telefunken 1937

Plate dissipation: 15W
Max plate voltage: 250V
Max cathode current: 90mA
Transconductance: 6mA/V

AD1

Characteristics

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

HeaterDirectly heated

Specifications of AD1 — Heater
Heater voltageVh	4 V
Heater currentIh	0.95 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of AD1 — Limiting values
Plate voltageVa max	250 V
Plate dissipationPa max	15 W
Cathode currentIk max	90 mA
Peak plate voltageVao	550 V

Mechanical

Specifications of AD1 — Mechanical
Base	P8A side-contact
Rarity	Legendary
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of AD1 — Small signal
Transconductance	6 mA/V
Plate resistance	670 Ω
Amplification factor	4

Charactereditorial reading, not a measurement

Specifications of AD1 — Character
Gain	4%
Power	38%
Drive	99%
Linearity	95%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	Va	Vg1 / Rk	Ia	Load	THD	gm	μ	Source
Class A, single-endedtriode connection · cathode bias	250 V	375 Ω	60 mA			6 mA/V	5	read on the sheet Philips / "Miniwatt" · 1947 · transcript
triode connection, single-endedclass not stated	250 V		60 mA	2.3 kΩ		6 mA/V	4	OCR, to be checked Philips "Miniwatt" · 1940 · p. 1 · transcript
Class A, push-pulltriode connection · fixed bias	250 V		60 mA		5%	6 mA/V	4	OCR, to be checked Philips / "Miniwatt" · 1947 · p. 3 · transcript

Design a stage →

Using this tube

Applications

SET output
Push-pull output
Headphone output

Generic triode power (se) stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Philips Miniwatt 1947/1953/1959 · Telefunken · Bulletin No. 30Active model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

5 manufacturer datasheets cross-checked for AD15 verified

Triode-connectedPhilips Radio~1937 (No. 30 bulletin; describes AD1 as "la nouvelle triode")

Vg1: -34 V
Ia: 15 mA
gm: 2 mA/V
Ra: 3000 Ω

AD1 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Philips Miniwatt 1947/1953/1959 · Telefunken · Bulletin No. 30
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The AD1 is a directly-heated triode from Philips·Telefunken, introduced around 1937. It provides a gain factor (μ) of 4 with 670Ω plate resistance. Commonly used in power (se) applications. Legendary European DHT. Queen of triodes.

History

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

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