What is the 71A vacuum tube?

The 71A is a triode vacuum tube designed for power (set) applications. Sub-watt SET. Intimate, delicate..

What is a 71A substitute or equivalent?

Direct equivalents to the 71A include 171A, VT-71A. 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 71A?

Amplification factor μ ≈ 3, transconductance gm ≈ 1.7 mA/V, plate resistance rp ≈ 1.8 kΩ, max plate voltage 180 V, max plate dissipation 4 W, heater 5 V / 0.25 A.

Is the 71A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 71A 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 71A sound like?

Sub-watt SET. Intimate, delicate.. 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.

71A Triode Vacuum Tube

Also known as 171A · VT-71A

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

TriodeHeater 5 V · 0.25 AUX-4RCA·Sylvania 1926

Plate dissipation: 4W
Max plate voltage: 180V
Amplification factor: 3
Transconductance: 1.7mA/V
Plate resistance: 1.75kΩ

71A

Characteristics

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

HeaterDirectly heated

Specifications of 71A — Heater
Heater voltageVh	5 V
Heater currentIh	0.25 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 71A — Limiting values
Plate voltageVa max	180 V
Plate dissipationPa max	4 W

Mechanical

Specifications of 71A — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 71A — Small signal
Transconductance	1.7 mA/V
Plate resistance	1.8 kΩ
Amplification factor	3

Capacitances

Specifications of 71A — Capacitances
Grid–cathode	3.2 pF
Grid–plate	7.5 pF
Plate–cathode	2.9 pF

Charactereditorial reading, not a measurement

Specifications of 71A — Character
Gain	3%
Power	10%
Drive	98%
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

Headphone output
Line stage

Generic triode power (set) stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

4 manufacturer datasheets cross-checked for 71A4 verified

71A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

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

Context

The 71A is a directly-heated triode from RCA·Sylvania, introduced around 1926. It provides a gain factor (μ) of 3 with 1750Ω plate resistance. Commonly used in power (set) applications. Sub-watt SET. Intimate, delicate.

History

Introduced: 1926
Manufacturer: RCA·Sylvania
Era: Pre-War

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