What is the 811A vacuum tube?

The 811A is a triode vacuum tube designed for transmitting applications. High-μ transmitting triode (μ=160) designed for class-B/C RF service. In audio it requires positive grid drive (zero-bias class-B) and is used in modulator stages..

What is a 811A substitute or equivalent?

Direct equivalents to the 811A include VT-144A. 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 811A?

Amplification factor μ ≈ 160, transconductance gm ≈ 4 mA/V, plate resistance rp ≈ 40.0 kΩ, max plate voltage 1500 V, max plate dissipation 65 W, heater 6.3 V / 4 A.

Is the 811A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 811A as Common 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 811A sound like?

High-μ transmitting triode (μ=160) designed for class-B/C RF service. In audio it requires positive grid drive (zero-bias class-B) and is used in modulator stages.. 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.

811A Triode Vacuum Tube

Also known as VT-144A

Power triode delivering 65W for push-pull and SET designs

TriodeHeater 6.3 V · 4 AUX-4 + Top CapRCA·GE 1940

Plate dissipation: 65W
Max plate voltage: 1500V
Transconductance: 4mA/V

811A

Characteristics

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

HeaterDirectly heated

Specifications of 811A — Heater
Heater voltageVh	6.3 V
Heater currentIh	4 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 811A — Limiting values
Plate voltageVa max	1500 V
Plate dissipationPa max	65 W

Mechanical

Specifications of 811A — Mechanical
Base	UX-4 + Top Cap
Rarity	Common
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 811A — Small signal
Transconductance	4 mA/V
Plate resistance	40 kΩ
Amplification factor	160

Capacitances

Specifications of 811A — Capacitances
Grid–cathode	5.9 pF
Grid–plate	5.6 pF
Plate–cathode	0.7 pF

Charactereditorial reading, not a measurement

Specifications of 811A — Character
Gain	100%
Power	100%
Drive	60%
Linearity	20%

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	Source
Class B, push-pulltriode connection · fixed bias	750 V	0 V	32 mA	OCR, to be checked RCA · 1963 · p. 1 · transcript

Model at this condition: Norman Koren Model
μ: 63.2
gm: 2.53 mA/V
rp: 24.9 kΩ

Using this tube

Applications

SET output
Push-pull output
High-gain preamp

Generic triode transmitting stage

Studio/recordingPA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : RCA 811A datasheet · Norman Koren SPICE model · cap audit 2026-05-09Active model : Norman Koren

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 811A1 verified

811A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA 811A datasheet · Norman Koren SPICE model · cap audit 2026-05-09
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The 811A is a transmitting triode originally designed for RF amplifier and modulator service, with a graphite plate and thoriated-tungsten filament. In audio use it can deliver 10-15W in single-ended Class A, though it is more commonly seen in push-pull configurations where it can produce 30-50W. Its relatively high mu (~35) for a power triode makes it easy to drive but gives it a less pure triode character than lower-mu DHTs like the 300B or 2A3. The 811A is inexpensive and readily available in current production, making it an accessible entry point to directly-heated triode amplification.

History

Introduced: 1940
Manufacturer: RCA·GE
Era: Pre-War

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