What is the 833A vacuum tube?

The 833A is a triode vacuum tube designed for transmitting (set) applications. Monster transmitting triode. 1kW capable..

What is a 833A substitute or equivalent?

Direct equivalents to the 833A include FU-33. 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 833A?

Amplification factor μ ≈ 35, transconductance gm ≈ 4 mA/V, plate resistance rp ≈ 7.8 kΩ, max plate voltage 4000 V, max plate dissipation 450 W, heater 10 V / 10 A.

Is the 833A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 833A as Sought-after 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 833A sound like?

Monster transmitting triode. 1kW capable.. 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

←833A

← 83 83V →Compare…

833A Triode Vacuum Tube

Triode10V / 10ASpecial

SourceRCA·GE·PentaReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Power triode delivering 450W for push-pull and SET designs

Datasheet ↗

833A — RCA·GE·Penta — triode vacuum tube — (1938)

7.8kΩ

4.0mA/V

12.3pF

6.3pF

8.50pF

GAIN35%

POWER100%

DRIVE92%

LINEARITY83%

SPECIFICATIONS

Heater10 V · 10 A

Max Plate Voltage4000 V

Pa max450 W

Gain Factor35

gm4 mA/V

rp7.8 kΩ

Inter-electrode capacitances

Cgk12.3 pF

Cgp6.3 pF

Cpk8.5 pF

PinoutSpecial

Era1938

RaritySought-after

HEATER10V / 10A

MAX PLATE4000V / 450W

BASEspecial

Source datasheets

4 manufacturer datasheets cross-checked for 833A

4 verified

EXECUTIVE SUMMARY

The 833A is a directly-heated triode from RCA·GE·Penta, introduced around 1938. It provides a gain factor (μ) of 35 with 7800Ω plate resistance. Commonly used in transmitting (set) applications. Monster transmitting triode. 1kW capable.

APPLICATIONS

SET outputPush-pull output

Generic triode transmitting (set) stage

• PA/public address

HISTORY

Introduced1938ManufacturerRCA·GE·Penta

Pre-War

833A Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

SIMILAR TRIODES

View all →

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