What is the CV591 vacuum tube?

The CV591 is a pentode vacuum tube designed for preamp applications. Military 6SJ7..

What is a CV591 substitute or equivalent?

Direct equivalents to the CV591 include 6SJ7 mil. 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 CV591?

Transconductance gm ≈ 1.65 mA/V, max plate voltage 300 V, max plate dissipation 2.5 W, heater 6.3 V / 0.3 A.

Is the CV591 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the CV591 as Moderate 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 CV591 sound like?

Military 6SJ7.. 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.

CV591 Pentode Vacuum Tube

Also known as 6SJ7 mil

Small-signal pentode for low-noise voltage amplification

PentodeHeater 6.3 V · 0.3 AOctalMullard 1942

Plate dissipation: 2.5W
Max plate voltage: 300V
Transconductance: 1.65mA/V

CV591

Characteristics

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

HeaterIndirectly heated

Specifications of CV591 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of CV591 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	2.5 W

Mechanical

Specifications of CV591 — Mechanical
Base	Octal
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of CV591 — Small signal
Transconductance	1.65 mA/V

Capacitances

Specifications of CV591 — Capacitances
Input	5 pF
Grid–plate	0.01 pF
Output	4 pF

Charactereditorial reading, not a measurement

Specifications of CV591 — Character
Gain	0%
Power	6%
Drive	50%
Linearity	75%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Using this tube

Applications

Voltage amplifier

Generic pentode preamp stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 9, 2026Source : audit-eu_a (CLEAN — matches canonical datasheet)Active model : Koren pentode

Manufacturer datasheets

CV591 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: audit-eu_a (CLEAN — matches canonical datasheet)
Reviewed: 2026-05-09
Status: DataModelCalc
Model: Koren pentode

Context

The CV591 is a indirectly-heated pentode from Mullard, introduced around 1942. Commonly used in preamp applications. Military 6SJ7.

History

Introduced: 1942
Manufacturer: Mullard
Era: Pre-War

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