What is the 307A vacuum tube?

The 307A (307A / VT-225) is a pentode vacuum tube designed for power/output applications. WE pentode. Triode-strapped yields 2A3-like tone..

What is a 307A substitute or equivalent?

Direct equivalents to the 307A include VT-225, RK-75. 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 307A?

Transconductance gm ≈ 4 mA/V, plate resistance rp ≈ 1.5 kΩ, max plate voltage 500 V, max plate dissipation 15 W, heater 5.5 V / 1 A.

Is the 307A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 307A 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 307A sound like?

WE pentode. Triode-strapped yields 2A3-like tone.. 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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307A 307A / VT-225 Pentode Vacuum Tube

Pentode5.5V / 1ASpecial

SourceWestern ElectricReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Power pentode delivering up to 15W in pentode, UL, or triode mode

Datasheet ↗

307A / VT-225 — Western Electric — pentode vacuum tube — (1938)

1.5kΩ

4.0mA/V

15.0pF

0.6pF

12.00pF

GAIN0%

POWER38%

DRIVE99%

LINEARITY75%

SPECIFICATIONS

Heater5.5 V · 1 A

Max Plate Voltage500 V

Pa max15 W

Gain Factor—

gm4 mA/V

rp1.5 kΩ

Inter-electrode capacitances

Cgk15 pF

Cgp0.55 pF

Cpk12 pF

PinoutSpecial

Era1938

RarityCollector

HEATER5.5V / 1A

MAX PLATE500V / 15W

BASEspecial

Source datasheets

1 manufacturer datasheets cross-checked for 307A / VT-225

1 verified

EXECUTIVE SUMMARY

The 307A is a directly-heated pentode from Western Electric, introduced around 1938. Commonly used in power/output applications. WE pentode. Triode-strapped yields 2A3-like tone.

APPLICATIONS

Power output

Generic pentode power/output stage

• Headphone amp

HISTORY

Introduced1938ManufacturerWestern Electric

Pre-War

307A 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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