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.

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..

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

TetrodeHeater 25 V · 7.15 A6-pin Special (transmitting) + Top CapUlyanovsk 1972

Plate dissipation: 140W
Max plate voltage: 33000V

GMI-90

Characteristics

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

HeaterIndirectly heated

Specifications of GMI-90 — Heater
Heater voltageVh	25 V
Heater currentIh	7.15 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of GMI-90 — Limiting values
Plate voltageVa max	33000 V
Plate dissipationPa max	140 W

Mechanical

Specifications of GMI-90 — Mechanical
Base	6-pin Special (transmitting) + Top Cap
Rarity	Rare
Pinout

Capacitances

Specifications of GMI-90 — Capacitances
Input	150 pF
Grid–plate	10 pF
Output	35 pF

Charactereditorial reading, not a measurement

Specifications of GMI-90 — Character
Gain	0%
Power	100%
Drive	50%
Linearity	75%

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

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

High-power output

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

PA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : ГМИ-90 primary datasheet (3.319.004 ТУ) · Том 18 Модуляторные лампы (1972) · УРЛЗ Ulyanovsk · external audit 2026-05-20

Manufacturer datasheets

1 manufacturer datasheets cross-checked for GMI-90 / ГМИ-901 verified

GMI-90 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: ГМИ-90 primary datasheet (3.319.004 ТУ) · Том 18 Модуляторные лампы (1972) · УРЛЗ Ulyanovsk · external audit 2026-05-20
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

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.

History

Introduced: 1972
Manufacturer: Ulyanovsk
Era: Late Production

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