What is the 01A vacuum tube?

The 01A (01A / 201A) is a triode vacuum tube designed for preamp applications. Dawn of audio. Thoriated tungsten charm..

What is a 01A substitute or equivalent?

Direct equivalents to the 01A include 201A, 301A, VT-30. 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 01A?

Amplification factor μ ≈ 8, transconductance gm ≈ 0.8 mA/V, plate resistance rp ≈ 10.0 kΩ, max plate voltage 135 V, max plate dissipation 1 W, heater 5 V / 0.25 A.

Is the 01A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 01A as Collector 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 01A sound like?

Dawn of audio. Thoriated tungsten charm.. 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

←01A

100TH →Compare…

01A 01A / 201A Triode Vacuum Tube

Triode5V / 0.25AUX-4

SourceRCA·GEReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Low-mu triode with excellent linearity for driver and line stages

Datasheet ↗

01A / 201A — RCA·GE — triode vacuum tube — (1924)

10.0kΩ

0.8mA/V

3.1pF

8.1pF

2.20pF

GAIN8%

POWER3%

DRIVE90%

LINEARITY95%

SPECIFICATIONS

Heater5 V · 0.25 A

Max Plate Voltage135 V

Pa max1 W

Gain Factor8

gm0.8 mA/V

rp10.0 kΩ

Inter-electrode capacitances

Cgk3.1 pF

Cgp8.1 pF

Cpk2.2 pF

PinoutUX-4

Era1924

RarityCollector

HEATER5V / 0.25A

MAX PLATE135V / 1W

BASEux4

Source datasheets

3 manufacturer datasheets cross-checked for 01A / 201A

3 verified

EXECUTIVE SUMMARY

The 01A is a directly-heated triode from RCA·GE, introduced around 1924. It provides a gain factor (μ) of 8 with 10.0kΩ plate resistance. Commonly used in preamp applications. Dawn of audio. Thoriated tungsten charm.

APPLICATIONS

Voltage amplifierLine stage

Generic triode preamp stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1924ManufacturerRCA·GE

Pre-War

01A 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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