What is a GU-50 substitute or equivalent?

Direct equivalents to the GU-50 include LS-50 / FU-50 (Telefunken originals); 807 is loose, not equivalent. 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 GU-50?

Transconductance gm ≈ 4 mA/V, max plate voltage 1000 V, max plate dissipation 40 W, heater 6.3 V / 0.705 A.

Is the GU-50 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the GU-50 as Common 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 GU-50 sound like?

Russian LS-50 / FU-50 family transmitting pentode; sometimes compared to 807, but not a direct equivalent.. 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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GU-50 Pentode Vacuum Tube

Q: What is the GU-50 vacuum tube?

The GU-50 is a pentode vacuum tube designed for transmitting applications. Russian LS-50 / FU-50 family transmitting pentode; sometimes compared to 807, but not a direct equivalent..

Pentode6.3V / 0.705ASpecialSPICE

SourceWikipedia GU-50 · OK1RR datasheet · wording corrected: 807 is loose comparison, not direct equivalentReviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

Power pentode delivering up to 40W in pentode, UL, or triode mode

Datasheet ↗SPICE

GU-50 — Russian — pentode vacuum tube — (1955)

4.0mA/V

14.0pF

0.1pF

9.70pF

GAIN0%

POWER100%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 0.705 A

Max Plate Voltage1000 V

Pa max40 W

Gain Factor—

gm4 mA/V

rp—

Inter-electrode capacitances

Cgk14 pF

Cgp0.1 pF

Cpk9.7 pF

PinoutSpecial

Era1955

RarityCommon

HEATER6.3V / 0.705A

MAX PLATE1000V / 40W

BASEspecial

Source datasheets

3 manufacturer datasheets cross-checked for GU-50

3 verified

EXECUTIVE SUMMARY

The GU-50 is a indirectly-heated pentode from Russian, introduced around 1955. Commonly used in transmitting applications. Russian LS-50 / FU-50 family transmitting pentode; sometimes compared to 807, but not a direct equivalent.

APPLICATIONS

Power output

Generic pentode transmitting stage

• PA/public address

HISTORY

Introduced1955ManufacturerRussian

Golden Age

GU-50 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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