What is the FU33 vacuum tube?

The FU33 (FU-33 / 833C) is a triode vacuum tube designed for transmitting (set) applications. Chinese 833A. Affordable transmitting triode power..

What is a FU33 substitute or equivalent?

Direct equivalents to the FU33 include 833A, 833C. 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 FU33?

Amplification factor μ ≈ 35, transconductance gm ≈ 4.5 mA/V, plate resistance rp ≈ 7.8 kΩ, max plate voltage 3000 V, max plate dissipation 350 W, heater 10 V / 10 A.

Is the FU33 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the FU33 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 FU33 sound like?

Chinese 833A. Affordable transmitting triode power.. 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

←FU33

← EL95 GI-7B →Compare → 833A

FU33 FU-33 / 833C Triode Vacuum Tube

Triode10V / 10ASpecial

SourceChineseReviewed—StatusDataModelCalcModelunder reviewPDF

Power triode delivering 350W for push-pull and SET designs

Datasheet ↗

FU-33 / 833C — Chinese — triode vacuum tube — (1965)

7.8kΩ

4.5mA/V

9.0pF

7.0pF

6.00pF

GAIN35%

POWER100%

DRIVE92%

LINEARITY83%

SPECIFICATIONS

Heater10 V · 10 A

Max Plate Voltage3000 V

Pa max350 W

Gain Factor35

gm4.5 mA/V

rp7.8 kΩ

Inter-electrode capacitances

Cgk9 pF

Cgp7 pF

Cpk6 pF

PinoutSpecial

Era1965

RarityCommon

HEATER10V / 10A

MAX PLATE3000V / 350W

BASEspecial

EXECUTIVE SUMMARY

The FU33 is a directly-heated triode from Chinese, introduced around 1965. It provides a gain factor (μ) of 35 with 7800Ω plate resistance. Commonly used in transmitting (set) applications. Chinese 833A. Affordable transmitting triode power.

APPLICATIONS

SET outputPush-pull output

Generic triode transmitting (set) stage

• PA/public address

VS 833A

μ 0%Rp +0%Pd -22%Full comparison →

HISTORY

Introduced1965ManufacturerChinese

Late Production

FU33 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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