What is the 47 vacuum tube?

The 47 is a pentode vacuum tube designed for power/output applications. Earliest power pentode. Pre-octal era output..

What is a 47 substitute or equivalent?

Direct equivalents to the 47 include VT-47, 247. 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 47?

Amplification factor μ ≈ 150, transconductance gm ≈ 2.5 mA/V, plate resistance rp ≈ 60.0 kΩ, max plate voltage 250 V, max plate dissipation 3.1 W, heater 2.5 V / 1.75 A.

Is the 47 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 47 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 47 sound like?

Earliest power pentode. Pre-octal era 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.

47 Pentode Vacuum Tube

Also known as VT-47 · 247

Small-signal pentode for low-noise voltage amplification

PentodeHeater 2.5 V · 1.75 AUX-5RCA·Sylvania 1931

Plate dissipation: 3.1W
Max plate voltage: 250V
Amplification factor: 150
Transconductance: 2.5mA/V
Plate resistance: 60kΩ

Characteristics

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

HeaterDirectly heated

Specifications of 47 — Heater
Heater voltageVh	2.5 V
Heater currentIh	1.75 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 47 — Limiting values
Plate voltageVa max	250 V
Screen voltageVg2 max	250 V
Plate dissipationPa max	3.1 W

Mechanical

Specifications of 47 — Mechanical
Base	UX-5
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 47 — Small signal
Transconductance	2.5 mA/V
Plate resistance	60 kΩ
Amplification factor	150

Capacitances

Specifications of 47 — Capacitances
Input	8.6 pF
Grid–plate	1.2 pF
Output	13 pF

Charactereditorial reading, not a measurement

Specifications of 47 — Character
Gain	100%
Power	8%
Drive	40%
Linearity	25%

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

Voltage amplifier

Generic pentode power/output stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

5 manufacturer datasheets cross-checked for 475 verified

47 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·Sylvania
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The 47 is a directly-heated pentode from RCA·Sylvania, introduced around 1931. It provides a gain factor (μ) of 150 with 60.0kΩ plate resistance. Commonly used in power/output applications. Earliest power pentode. Pre-octal era output.

History

Introduced: 1931
Manufacturer: RCA·Sylvania
Era: Pre-War

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