What is the 27 vacuum tube?

The 27 (27 / UY-227) is a triode vacuum tube designed for preamp applications. First indirectly heated triode. Ancestor of 6SN7..

What is a 27 substitute or equivalent?

Direct equivalents to the 27 include VT-29. 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 27?

Amplification factor μ ≈ 9, transconductance gm ≈ 0.975 mA/V, plate resistance rp ≈ 9.3 kΩ, max plate voltage 275 V, max plate dissipation 2 W, heater 2.5 V / 1.75 A.

Is the 27 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 27 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 27 sound like?

First indirectly heated triode. Ancestor of 6SN7.. 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

←27

← 26 274B →Compare…

27 27 / UY-227 Triode Vacuum Tube

Triode2.5V / 1.75AUX-5SPICE

SourceRCA·GEReviewed2026-05-29StatusDataModelCalcModelAyumi NakabayashiPDF

Low-mu triode with excellent linearity for driver and line stages

Datasheet ↗SPICE

27 / UY-227 — RCA·GE — triode vacuum tube — (1927)

9.3kΩ

1.0mA/V

3.1pF

3.3pF

2.30pF

GAIN9%

POWER5%

DRIVE91%

LINEARITY95%

SPECIFICATIONS

Heater2.5 V · 1.75 A

Max Plate Voltage275 V

Pa max2 W

Gain Factor9

gm0.975 mA/V

rp9.3 kΩ

Inter-electrode capacitances

Cgk3.1 pF

Cgp3.3 pF

Cpk2.3 pF

PinoutUX-5

Era1927

RarityCollector

HEATER2.5V / 1.75A

MAX PLATE275V / 2W

BASEux5

Source datasheets

5 manufacturer datasheets cross-checked for 27 / UY-227

5 verified

TYPICAL OPERATING POINT

Va135V

Ia2.35mA

Vg-11V

Pd0.32W

RL19kΩ

Av14.6dB

EXECUTIVE SUMMARY

The 27 is a indirectly-heated triode from RCA·GE, introduced around 1927. It provides a gain factor (μ) of 9 with 9250Ω plate resistance. Commonly used in preamp applications. First indirectly heated triode. Ancestor of 6SN7.

APPLICATIONS

Voltage amplifierLine stage

Generic triode preamp stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1927ManufacturerRCA·GE

Pre-War

27 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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