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.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

←47

← 46 4P1L →Compare…

47 Pentode Vacuum Tube

Pentode2.5V / 1.75AUX-5

SourceRCA·SylvaniaReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Small-signal pentode for low-noise voltage amplification

Datasheet ↗

47 — RCA·Sylvania — pentode vacuum tube — (1931)

150

60.0kΩ

2.5mA/V

8.6pF

1.2pF

13.00pF

GAIN100%

POWER8%

DRIVE40%

LINEARITY25%

SPECIFICATIONS

Heater2.5 V · 1.75 A

Max Plate Voltage250 V

Pa max3.1 W

Gain Factor150

gm2.5 mA/V

rp60.0 kΩ

Inter-electrode capacitances

Cgk8.6 pF

Cgp1.2 pF

Cpk13 pF

PinoutUX-5

Era1931

RaritySought-after

HEATER2.5V / 1.75A

MAX PLATE250V / 3.1W

BASEux5

Source datasheets

5 manufacturer datasheets cross-checked for 47

5 verified

EXECUTIVE SUMMARY

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.

APPLICATIONS

Voltage amplifier

Generic pentode power/output stage

HISTORY

Introduced1931ManufacturerRCA·Sylvania

Pre-War

47 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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