What is the 7581A vacuum tube?

The 7581A is a tetrode vacuum tube designed for power (pp) applications. Ruggedized 6L6GC. Balanced, detailed..

What is a 7581A substitute or equivalent?

Direct equivalents to the 7581A include 6L6GC (ruggedized). 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 7581A?

Amplification factor μ ≈ 8, transconductance gm ≈ 6 mA/V, plate resistance rp ≈ 22.5 kΩ, max plate voltage 500 V, max plate dissipation 35 W, heater 6.3 V / 0.9 A.

Is the 7581A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 7581A 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 7581A sound like?

Ruggedized 6L6GC. Balanced, detailed.. 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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7581A Tetrode Vacuum Tube

Tetrode6.3V / 0.9AOctal

SourceTung-Sol·GEReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Beam power tetrode rated at 35W for high-power output stages

Datasheet ↗

7581A — Tung-Sol·GE — tetrode vacuum tube — (1960)

22.5kΩ

6.0mA/V

10.0pF

0.6pF

6.50pF

GAIN8%

POWER88%

DRIVE78%

LINEARITY95%

SPECIFICATIONS

Heater6.3 V · 0.9 A

Max Plate Voltage500 V

Pa max35 W

Gain Factor8

gm6 mA/V

rp22.5 kΩ

Inter-electrode capacitances

Cgk10 pF

Cgp0.6 pF

Cpk6.5 pF

PinoutOctal

Era1960

RaritySought-after

HEATER6.3V / 0.9A

MAX PLATE500V / 35W

BASEoctal

Source datasheets

2 manufacturer datasheets cross-checked for 7581A

2 verified

EXECUTIVE SUMMARY

The 7581A is a indirectly-heated beam tetrode from Tung-Sol·GE, introduced around 1960. It provides a gain factor (μ) of 8 with 22.5kΩ plate resistance. Commonly used in power (pp) applications. Ruggedized 6L6GC. Balanced, detailed.

APPLICATIONS

High-power output

Generic tetrode power (pp) stage

• PA/public address

HISTORY

Introduced1960ManufacturerTung-Sol·GE

Late Production

7581A 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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