What is the 50 vacuum tube?

The 50 is a triode vacuum tube designed for power (set) applications. Between 2A3 and 300B. Powerful DHT SET output..

What is a 50 substitute or equivalent?

Direct equivalents to the 50 include VT-50. 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 50?

Amplification factor μ ≈ 4, transconductance gm ≈ 2.1 mA/V, plate resistance rp ≈ 1.8 kΩ, max plate voltage 450 V, max plate dissipation 25 W, heater 7.5 V / 1.25 A.

Is the 50 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 50 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 50 sound like?

Between 2A3 and 300B. Powerful DHT SET output.. 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

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50 Triode Vacuum Tube

Triode7.5V / 1.25AUX-4SPICE

SourceRCA·GEReviewed2026-05-29StatusDataModelCalcModelAyumi NakabayashiPDF

High-power directly-heated triode for single-ended amplification

Datasheet ↗SPICE

50 — RCA·GE — triode vacuum tube — (1928)

1.8kΩ

2.1mA/V

4.2pF

7.1pF

3.40pF

GAIN4%

POWER63%

DRIVE98%

LINEARITY95%

SPECIFICATIONS

Heater7.5 V · 1.25 A

Max Plate Voltage450 V

Pa max25 W

Gain Factor4

gm2.1 mA/V

rp1.8 kΩ

Inter-electrode capacitances

Cgk4.2 pF

Cgp7.1 pF

Cpk3.4 pF

PinoutUX-4

Era1928

RarityCollector

HEATER7.5V / 1.25A

MAX PLATE450V / 25W

BASEux4

Source datasheets

5 manufacturer datasheets cross-checked for 50

5 verified

TYPICAL OPERATING POINT

Va375V

Ia58.55mA

Vg-58.56399999999999V

Pd21.96W

RL4kΩ

Av8.3dB

EXECUTIVE SUMMARY

The 50 is a directly-heated triode from RCA·GE, introduced around 1928. It provides a gain factor (μ) of 4 with 1800Ω plate resistance. Commonly used in power (set) applications. Between 2A3 and 300B. Powerful DHT SET output.

APPLICATIONS

SET outputPush-pull outputHeadphone output

Generic triode power (set) stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1928ManufacturerRCA·GE

Pre-War

50 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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