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.

50 Triode Vacuum Tube

Also known as VT-50

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

TriodeHeater 7.5 V · 1.25 AUX-4RCA·GE 1928

Plate dissipation: 25W
Max plate voltage: 450V
Transconductance: 2.1mA/V

Characteristics

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

HeaterDirectly heated

Specifications of 50 — Heater
Heater voltageVh	7.5 V
Heater currentIh	1.25 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 50 — Limiting values
Plate voltageVa max	450 V
Plate dissipationPa max	25 W

Mechanical

Specifications of 50 — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 50 — Small signal
Transconductance	2.1 mA/V
Plate resistance	1.8 kΩ
Amplification factor	4

Capacitances

Specifications of 50 — Capacitances
Grid–cathode	4.2 pF
Grid–plate	7.1 pF
Plate–cathode	3.4 pF

Charactereditorial reading, not a measurement

Specifications of 50 — Character
Gain	4%
Power	63%
Drive	98%
Linearity	95%

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	Load	Pout	gm	μ	rp	Source
Class A, single-endedtriode connection · fixed bias	300 V	-54 V	35 mA	4.6 kΩ	1.6 W	1.9 mA/V	3.8	2 kΩ	OCR, to be checked Tung-Sol · 1940 · p. 1 · transcript

Model at this condition: Ayumi Nakabayashi Model
μ: 3.6
gm: 1.51 mA/V
rp: 2.4 kΩ

Using this tube

Applications

SET output
Push-pull output
Headphone output

Generic triode power (set) stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Active model : Ayumi Nakabayashi

Manufacturer datasheets

5 manufacturer datasheets cross-checked for 505 verified

50 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·GE
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi

Context

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.

History

Introduced: 1928
Manufacturer: RCA·GE
Era: Pre-War

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