What is the VT-91 vacuum tube?

The VT-91 is a triode vacuum tube designed for preamp applications. Military 6J7..

What is a VT-91 substitute or equivalent?

Direct equivalents to the VT-91 include 6J7 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 VT-91?

Amplification factor μ ≈ 20, transconductance gm ≈ 2.6 mA/V, plate resistance rp ≈ 7.7 kΩ, max plate voltage 300 V, max plate dissipation 2.5 W, heater 6.3 V / 0.3 A.

Is the VT-91 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the VT-91 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 VT-91 sound like?

Military 6J7.. 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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VT-91 Triode Vacuum Tube

Triode6.3V / 0.3ASmall Wafer Octal 6-Pin (6J5/B6-23)SPICE

Sourcevacuumtubes.io 6J7 (= VT-91)Reviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

Medium-gain triode for driver and line stage applications

Datasheet ↗SPICE

VT-91 — RCA — triode vacuum tube — (1942)

7.7kΩ

2.6mA/V

3.4pF

3.60pF

GAIN20%

POWER6%

DRIVE92%

LINEARITY90%

SPECIFICATIONS

Heater6.3 V · 0.3 A

Max Plate Voltage300 V

Pa max2.5 W

Gain Factor20

gm2.6 mA/V

rp7.7 kΩ

Inter-electrode capacitances

Cgk3.4 pF

Cgp3.4 pF

Cpk3.6 pF

PinoutSmall Wafer Octal 6-Pin (6J5/B6-23)

Era1942

RarityModerate

HEATER6.3V / 0.3A

MAX PLATE300V / 2.5W

BASEspecial-6

Source datasheets

6 manufacturer datasheets cross-checked for VT-91

6 verified

EXECUTIVE SUMMARY

The VT-91 is a indirectly-heated triode from RCA, introduced around 1942. It provides a gain factor (μ) of 20 with 7700Ω plate resistance. Commonly used in preamp applications. Military 6J7.

APPLICATIONS

Voltage amplifier

Generic triode preamp stage

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1942ManufacturerRCA

Pre-War

VT-91 Datasheet

Local mirror · PDF

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METRIX TESTER

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