What is the GM70 vacuum tube?

The GM70 is a triode vacuum tube designed for transmitting (set) applications. Russian transmitting. Enormous..

What is a GM70 substitute or equivalent?

Direct equivalents to the GM70 include 845 (closer functional equivalent than GK-71). 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 GM70?

Amplification factor μ ≈ 7, transconductance gm ≈ 6 mA/V, plate resistance rp ≈ 1.2 kΩ, max plate voltage 1500 V, max plate dissipation 125 W, heater 20 V / 3 A.

Is the GM70 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the GM70 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 GM70 sound like?

Russian transmitting. Enormous.. 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.

GM70 Triode Vacuum Tube

Also known as 845 (closer functional equivalent than GK-71)

Power triode delivering 125W for push-pull and SET designs

TriodeHeater 20 V · 3 A4-pin Soviet septarRussian 1960

Plate dissipation: 125W
Max plate voltage: 1500V
Transconductance: 6mA/V

GM70

Characteristics

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

HeaterDirectly heated

Specifications of GM70 — Heater
Heater voltageVh	20 V
Heater currentIh	3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of GM70 — Limiting values
Plate voltageVa max	1500 V
Plate dissipationPa max	125 W

Mechanical

Specifications of GM70 — Mechanical
Base	4-pin Soviet septar
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of GM70 — Small signal
Transconductance	6 mA/V
Plate resistance	1.2 kΩ
Amplification factor	7

Capacitances

Specifications of GM70 — Capacitances
Grid–cathode	8 pF
Grid–plate	12 pF
Plate–cathode	4 pF

Charactereditorial reading, not a measurement

Specifications of GM70 — Character
Gain	7%
Power	100%
Drive	99%
Linearity	95%

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

Using this tube

Applications

SET output
Push-pull output
Headphone output

Generic triode transmitting (set) stage

Headphone ampPA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Soviet-Tubes GM-70 · jacmusic GM70 · cap audit 2026-05-09Active model : Norman Koren

Manufacturer datasheets

2 manufacturer datasheets cross-checked for GM702 verified

GM70 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Soviet-Tubes GM-70 · jacmusic GM70 · cap audit 2026-05-09
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The GM70 is a Russian directly-heated transmitting triode with a thoriated-tungsten filament, capable of delivering 20-30W in single-ended Class A at plate voltages of 800-1200V. It is the Soviet equivalent of the Western 211/845 family, with a characteristically bold, fast, and slightly lean sonic signature. The graphite plate construction gives it high plate dissipation capability and a distinctive visual appearance. The GM70 has become popular in high-end SET designs, particularly from Chinese and Japanese manufacturers, as a cost-effective alternative to NOS Western transmitting triodes.

History

Introduced: 1960
Manufacturer: Russian
Era: Late Production

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