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.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

←AD1

← A2134 AZ1 →Compare…

AD1 Triode Vacuum Tube

Triode4V / 0.95AP8A side-contactSPICE

SourcePhilips Miniwatt 1947/1953/1959 · Telefunken · Bulletin No. 30Reviewed2026-05-29StatusDataModelCalcModel2 enginesPDF

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

Datasheet ↗SPICE

AD1 — Philips·Telefunken — triode vacuum tube — (1937)

670Ω

6.0mA/V

GAIN4%

POWER38%

DRIVE99%

LINEARITY95%

SPECIFICATIONS

Heater4 V · 0.95 A

Max Plate Voltage250 V

Pa max15 W

Gain Factor4

gm6 mA/V

rp670 Ω

PinoutP8A side-contact

Era1937

RarityLegendary

HEATER4V / 0.95A

MAX PLATE250V / 15W

BASEp8a-sc

Source datasheets

5 manufacturer datasheets cross-checked for AD1

5 verified

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

Specs when the screen grid (g2) is tied to the anode — the tube acts as a triode.

Vg1

-34 V

15 mA

2 mA/V

3000 Ω

According to Philips Radio (application bulletin "No. 30", French) (~1937 (No. 30 bulletin; describes AD1 as "la nouvelle triode")): « triode-connected »

TYPICAL OPERATING POINT

SPICE model(2 available)1 .subckt available ↓

Va225V

Ia57.73mA

Vg-38.97434199999999V

Pd12.99W

RL2kΩ

Av10.8dB

EXECUTIVE SUMMARY

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.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (se) stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1937ManufacturerPhilips·Telefunken

Pre-War

AD1 Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

SIMILAR TRIODES

View all →

01APreamp 100THTransmitting (SET)101DPower (SET)10YPower (SET)12AT7Driver 12AU7Line / Headphone 12AX7Preamp 12AY7Preamp