What is the 5U4G vacuum tube?

The 5U4G (5U4G / 5U4GB) is a rectifier vacuum tube designed for rectifier applications. Softer delivery adds warmth..

What is a 5U4G substitute or equivalent?

Direct equivalents to the 5U4G include CV593. 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.

Is the 5U4G still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 5U4G 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 5U4G sound like?

Softer delivery adds warmth.. 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.

5U4G 5U4GB Rectifier Vacuum Tube

Also known as CV593

Full-wave rectifier for vacuum tube power supply designs

RectifierHeater 5 V · 3 AOctalRCA·Sylvania 1940

Max DC output current: 225mA
Peak inverse voltage: 1550V
Max RMS input per anode: 550V
Peak anode current: 675mA

5U4G

Characteristics

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

HeaterDirectly heated

Specifications of 5U4G — Heater
Heater voltageVh	5 V
Heater currentIh	3 A

Rectifier limitsDatasheet maximum ratings — not to be exceeded

Specifications of 5U4G — Rectifier limits
Max RMS input voltage per anode	550 V
Io max (DC output current)	225 mA
Peak inverse voltage (PIV)	1550 V
Peak anode current	675 mA
Tube voltage drop at Io	58 V at 225 mA
Max reservoir capacitor	32 µF
Min series resistance per anode	75 Ω

Mechanical

Specifications of 5U4G — Mechanical
Base	Octal
Rarity	Common
Pinout

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

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

Power supply rectification

Fender Tweed power supplyDynaco ST-70 PSU

Guitar ampHeadphone amp

Featured in these amplifiers

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : RCA·Sylvania datasheet · cap audit 2026-05-09

Manufacturer datasheets

4 manufacturer datasheets cross-checked for 5U4G / 5U4GB4 verified

5U4G DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·Sylvania datasheet · cap audit 2026-05-09
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The 5U4G is a full-wave vacuum rectifier with a directly-heated cathode, rated for up to 275mA output current. It provides a relatively soft, gradual power supply characteristic with moderate voltage drop (~40-50V under load), which contributes to the dynamic, spongy feel in amplifiers that use it. The 5U4G's compliant power supply behavior is part of the sound in classic amplifiers like the Fender Tweed Bassman and many early hi-fi designs. RCA, GE, Tung-Sol, and Sylvania all made reliable examples; it is one of the most commonly encountered rectifier tubes in American amplifier designs of the 1950s and 60s.

History

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

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