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.

VT-91 Triode Vacuum Tube

Also known as 6J7 mil

Medium-gain triode for driver and line stage applications

TriodeHeater 6.3 V · 0.3 ASmall Wafer Octal 6-Pin (6J5/B6-23)RCA 1942

Plate dissipation: 2.5W
Max plate voltage: 300V
Amplification factor: 20
Transconductance: 2.6mA/V
Plate resistance: 7.7kΩ

VT-91

Characteristics

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

HeaterIndirectly heated

Specifications of VT-91 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of VT-91 — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	2.5 W
Cathode currentIk max	20 mA
Grid resistorRg1 max	1 MΩ
Heater–cathode voltageVhk max	100 V

Mechanical

Specifications of VT-91 — Mechanical
Base	Small Wafer Octal 6-Pin (6J5/B6-23)
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of VT-91 — Small signal
Transconductance	2.6 mA/V
Plate resistance	7.7 kΩ
Amplification factor	20

Capacitances

Specifications of VT-91 — Capacitances
Grid–cathode	3.4 pF
Grid–plate	3.4 pF
Plate–cathode	3.6 pF

Charactereditorial reading, not a measurement

Specifications of VT-91 — Character
Gain	20%
Power	6%
Drive	92%
Linearity	90%

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

Using this tube

Applications

Voltage amplifier

Generic triode preamp stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : vacuumtubes.io 6J7 (= VT-91)Active model : Koren pentode

Manufacturer datasheets

6 manufacturer datasheets cross-checked for VT-916 verified

VT-91 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: vacuumtubes.io 6J7 (= VT-91)
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren pentode

Context

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.

History

Introduced: 1942
Manufacturer: RCA
Era: Pre-War

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