What is a GMI-90 substitute or equivalent?

Direct equivalents to the GMI-90 include None — high-voltage pulse-modulator class. 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 GMI-90?

Max plate voltage 33000 V, max plate dissipation 140 W, heater 25 V / 7.15 A.

Is the GMI-90 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the GMI-90 as Rare 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.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

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GMI-90 GMI-90 / ГМИ-90 Tetrode Vacuum Tube

Q: What is the GMI-90 vacuum tube?

The GMI-90 (GMI-90 / ГМИ-90) is a tetrode vacuum tube designed for pulse modulator (transmitting) — not for audio applications. Massive Soviet pulse-modulator beam tetrode (генераторный лучевой тетрод) for radar / high-energy switching. Indirectly-heated oxide cathode (25 V / 6.5–7.8 A); top-cap anode, 6-pin transmitting base; forced-air cooling mandatory; 300 s minimum heat-up. Built at the Ulyanovsk Radio Lamp Plant (УРЛЗ). NOT designed for audio service — listed here for completeness; community SE/PSE conversions exist (Vietnam SUMO 2009, ~25 W/channel) but lack published curves and measurements..

Tetrode25V / 7.15A6-pin Special (transmitting) + Top Cap

SourceГМИ-90 primary datasheet (3.319.004 ТУ) · Том 18 Модуляторные лампы (1972) · УРЛЗ Ulyanovsk · external audit 2026-05-20Reviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Beam power tetrode rated at 140W for high-power output stages

Datasheet ↗

GMI-90 / ГМИ-90 — Ulyanovsk — tetrode vacuum tube — (1972)

150.0pF

10.0pF

35.00pF

GAIN0%

POWER100%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater25 V · 7.15 A

Max Plate Voltage33000 V

Pa max140 W

Gain Factor—

gm—

rp—

Inter-electrode capacitances

Cgk150 pF

Cgp10 pF

Cpk35 pF

Pinout6-pin Special (transmitting) + Top Cap

Era1972

RarityRare

HEATER25V / 7.15A

MAX PLATE33000V / 140W

BASEspecial-6

Source datasheets

1 manufacturer datasheets cross-checked for GMI-90 / ГМИ-90

1 verified

EXECUTIVE SUMMARY

The GMI-90 is a indirectly-heated beam tetrode from Ulyanovsk, introduced around 1972. Commonly used in pulse modulator (transmitting) — not for audio applications. Massive Soviet pulse-modulator beam tetrode (генераторный лучевой тетрод) for radar / high-energy switching. Indirectly-heated oxide cathode (25 V / 6.5–7.8 A); top-cap anode, 6-pin transmitting base; forced-air cooling mandatory; 300 s minimum heat-up. Built at the Ulyanovsk Radio Lamp Plant (УРЛЗ). NOT designed for audio service — listed here for completeness; community SE/PSE conversions exist (Vietnam SUMO 2009, ~25 W/channel) but lack published curves and measurements.

APPLICATIONS

High-power output

Generic tetrode pulse modulator (transmitting) — not for audio stage

• PA/public address

HISTORY

Introduced1972ManufacturerUlyanovsk

Late Production

GMI-90 Datasheet

Local mirror · PDF

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METRIX TESTER

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