What is the 4Y75R vacuum tube?

The 4Y75R is a tetrode vacuum tube designed for output power applications.

What is a 4Y75R substitute or equivalent?

Direct equivalents to the 4Y75R include EL156. 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 4Y75R?

Amplification factor μ ≈ 4, transconductance gm ≈ 10 mA/V, max plate voltage 800 V, max plate dissipation 35 W, heater 6.3 V / 1.65 A.

Is the 4Y75R still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 4Y75R 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.

What does the 4Y75R sound like?

Sonic character depends 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.

4Y75R Tetrode Vacuum Tube

Also known as EL156

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

TetrodeHeater 6.3 V · 1.65 AOctalMullard 1960

Plate dissipation: 35W
Max plate voltage: 800V
Max screen voltage: 400V
Max cathode current: 200mA
Transconductance: 10mA/V

4Y75R

Characteristics

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

HeaterIndirectly heated

Specifications of 4Y75R — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.65 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 4Y75R — Limiting values
Plate voltageVa max	800 V
Screen voltageVg2 max	400 V
Plate dissipationPa max	35 W
Screen dissipationPg2 max	4.5 W
Cathode currentIk max	200 mA

Mechanical

Specifications of 4Y75R — Mechanical
Base	Octal
Rarity	Rare

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 4Y75R — Small signal
Transconductance	10 mA/V
Amplification factor	4

Capacitances

Specifications of 4Y75R — Capacitances
Input	18 pF
Grid–plate	1.2 pF
Output	15 pF

Charactereditorial reading, not a measurement

Specifications of 4Y75R — Character
Gain	4%
Power	88%
Drive	50%
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 output power stage

PA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

2 manufacturer datasheets cross-checked for 4Y75R2 verified

4Y75R DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Mullard
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The 4Y75R is a indirectly-heated beam tetrode from Mullard, introduced around 1960. Commonly used in output power applications.

History

Introduced: 1960
Manufacturer: Mullard
Era: Late Production

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