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.

01A 201A Triode Vacuum Tube

Also known as 201A · 301A · VT-30

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

TriodeHeater 5 V · 0.25 AUX-4RCA·GE 1924

Plate dissipation: 1W
Max plate voltage: 135V
Amplification factor: 8
Transconductance: 0.8mA/V
Plate resistance: 10kΩ

01A

Characteristics

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

HeaterDirectly heated

Specifications of 01A — Heater
Heater voltageVh	5 V
Heater currentIh	0.25 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 01A — Limiting values
Plate voltageVa max	135 V
Plate dissipationPa max	1 W

Mechanical

Specifications of 01A — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 01A — Small signal
Transconductance	0.8 mA/V
Plate resistance	10 kΩ
Amplification factor	8

Capacitances

Specifications of 01A — Capacitances
Grid–cathode	3.1 pF
Grid–plate	8.1 pF
Plate–cathode	2.2 pF

Charactereditorial reading, not a measurement

Specifications of 01A — Character
Gain	8%
Power	3%
Drive	90%
Linearity	95%

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

Using this tube

No interactive loadline model for this tube yet — download a SPICE model below to simulate it in LTspice or ngspice.

Applications

Voltage amplifier
Line stage

Generic triode preamp stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

3 manufacturer datasheets cross-checked for 01A / 201A3 verified

01A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·GE
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

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.

History

Introduced: 1924
Manufacturer: RCA·GE
Era: Pre-War

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