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.

307A VT-225 Pentode Vacuum Tube

Also known as VT-225 · RK-75

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

PentodeHeater 5.5 V · 1 ASpecialWestern Electric 1938

Plate dissipation: 15W
Max plate voltage: 500V
Transconductance: 4mA/V

307A

Characteristics

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

HeaterDirectly heated

Specifications of 307A — Heater
Heater voltageVh	5.5 V
Heater currentIh	1 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 307A — Limiting values
Plate voltageVa max	500 V
Plate dissipationPa max	15 W

Mechanical

Specifications of 307A — Mechanical
Base	Special
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 307A — Small signal
Transconductance	4 mA/V
Plate resistance	1.5 kΩ

Capacitances

Specifications of 307A — Capacitances
Input	15 pF
Grid–plate	0.55 pF
Output	12 pF

Charactereditorial reading, not a measurement

Specifications of 307A — Character
Gain	0%
Power	38%
Drive	99%
Linearity	75%

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

Power output

Generic pentode power/output stage

Headphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 307A / VT-2251 verified

307A DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Western Electric
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

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.

History

Introduced: 1938
Manufacturer: Western Electric
Era: Pre-War

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