What is the EL509 vacuum tube?

The EL509 (EL509 / 6KG6) is a tetrode vacuum tube designed for power (se/pp) applications. High-power sweep pentode. Massive headroom..

What is a EL509 substitute or equivalent?

Direct equivalents to the EL509 include 6KG6. 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 EL509?

Amplification factor μ ≈ 10, transconductance gm ≈ 18 mA/V, plate resistance rp ≈ 8.0 kΩ, max plate voltage 700 V, max plate dissipation 35 W, heater 6.3 V / 2 A.

Is the EL509 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the EL509 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 EL509 sound like?

High-power sweep pentode. Massive headroom.. 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.

EL509 6KG6 Tetrode Vacuum Tube

Also known as 6KG6

Beam power tetrode rated at 35W for high-power output stages

TetrodeHeater 6.3 V · 2 AMagnoval + Top CapPhilips·Svetlana 1963

Plate dissipation: 35W
Max plate voltage: 700V
Max screen voltage: 700V
Max cathode current: 500mA
Transconductance: 18mA/V

EL509

Characteristics

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

HeaterIndirectly heated

Specifications of EL509 — Heater
Heater voltageVh	6.3 V
Heater currentIh	2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of EL509 — Limiting values
Plate voltageVa max	700 V
Screen voltageVg2 max	700 V
Plate dissipationPa max	35 W
Screen dissipationPg2 max	7 W
Cathode currentIk max	500 mA
Grid resistorRg1 max	500 kΩ
Heater–cathode voltageVhk max	250 V

Mechanical

Specifications of EL509 — Mechanical
Base	Magnoval + Top Cap
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of EL509 — Small signal
Transconductance	18 mA/V
Plate resistance	8 kΩ
Amplification factor	10

Capacitances

Specifications of EL509 — Capacitances
Input	25 pF
Grid–plate	2.5 pF
Output	9 pF

Charactereditorial reading, not a measurement

Specifications of EL509 — Character
Gain	10%
Power	88%
Drive	92%
Linearity	95%

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 power (se/pp) stage

PA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Frank/pocnet EL509 datasheet · vacuumtubesinc · cap audit 2026-05-09

Manufacturer datasheets

4 manufacturer datasheets cross-checked for EL509 / 6KG64 verified

EL509 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Frank/pocnet EL509 datasheet · vacuumtubesinc · cap audit 2026-05-09
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The EL509 is a indirectly-heated beam tetrode from Philips·Svetlana, introduced around 1963. It provides a gain factor (μ) of 10 with 8000Ω plate resistance. Commonly used in power (se/pp) applications. High-power sweep pentode. Massive headroom.

History

Introduced: 1963
Manufacturer: Philips·Svetlana
Era: Late Production

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