What is the 5998 vacuum tube?

The 5998 is a triode vacuum tube designed for power/output applications. OTL king. Muscular current delivery..

What is a 5998 substitute or equivalent?

Direct equivalents to the 5998 include 421A, 7236. 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 5998?

Amplification factor μ ≈ 6, transconductance gm ≈ 14 mA/V, plate resistance rp ≈ 350 Ω, max plate voltage 275 V, max plate dissipation 15 W, heater 6.3 V / 2.4 A.

Is the 5998 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 5998 as Sought-after 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 5998 sound like?

OTL king. Muscular current delivery.. 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.

5998 Triode Vacuum Tube

Also known as 421A · 7236

Power triode delivering 15W for push-pull and SET designs

Dual triodeHeater 6.3 V · 2.4 AOctal2 sectionsTung-Sol 1953

Plate dissipation: 15W
Max plate voltage: 275V
Transconductance: 14mA/V

5998

Characteristics

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

HeaterIndirectly heated

Specifications of 5998 — Heater
Heater voltageVh	6.3 V
Heater currentIh	2.4 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 5998 — Limiting values
Plate voltageVa max	275 V
Plate dissipationPa max	15 W

Mechanical

Specifications of 5998 — Mechanical
Base	Octal
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 5998 — Small signal
Transconductance	14 mA/V
Plate resistance	350 Ω
Amplification factor	6

Capacitances

Specifications of 5998 — Capacitances
Grid–cathode	7.7 pF
Grid–plate	18.3 pF
Plate–cathode	2.5 pF

Charactereditorial reading, not a measurement

Specifications of 5998 — Character
Gain	6%
Power	38%
Drive	100%
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
Phase splitter

Generic triode power/output stage

Hi-Fi stereoHeadphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Active model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 59981 verified

5998 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Tung-Sol
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The 5998 is a dual indirectly-heated triode from Tung-Sol, introduced around 1953. It provides a gain factor (μ) of 6 with 350Ω plate resistance. Commonly used in power/output applications. OTL king. Muscular current delivery.

History

Introduced: 1953
Manufacturer: Tung-Sol
Era: Golden Age

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