What is the 100TH vacuum tube?

The 100TH (100TH / VT-218) is a triode vacuum tube designed for transmitting (set) applications. High-mu Eimac transmitting triode. Needs power drive..

What is a 100TH substitute or equivalent?

Direct equivalents to the 100TH include VT-218. 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 100TH?

Amplification factor μ ≈ 38, transconductance gm ≈ 4.5 mA/V, plate resistance rp ≈ 8.4 kΩ, max plate voltage 3000 V, max plate dissipation 100 W, heater 5 V / 6.3 A.

Is the 100TH still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 100TH 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 100TH sound like?

High-mu Eimac transmitting triode. Needs power drive.. 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

←100TH

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100TH 100TH / VT-218 Triode Vacuum Tube

Triode5V / 6.3AUX-4SPICE

SourceEimac 100TH datasheet (Eitel-McCullough, San Bruno CA)Reviewed2026-05-29StatusDataModelCalcModelAyumi NakabayashiPDF

Power triode delivering 100W for push-pull and SET designs

Datasheet ↗SPICE

100TH / VT-218 — Eimac — triode vacuum tube — (1938)

8.4kΩ

4.5mA/V

2.9pF

2.0pF

0.30pF

GAIN38%

POWER100%

DRIVE92%

LINEARITY81%

SPECIFICATIONS

Heater5 V · 6.3 A

Max Plate Voltage3000 V

Pa max100 W

Gain Factor38

gm4.5 mA/V

rp8.4 kΩ

Inter-electrode capacitances

Cgk2.9 pF

Cgp2 pF

Cpk0.3 pF

PinoutUX-4

Era1938

RarityRare

HEATER5V / 6.3A

MAX PLATE3000V / 100W

BASEux4

Source datasheets

2 manufacturer datasheets cross-checked for 100TH / VT-218

2 verified

TYPICAL OPERATING POINT

Va1500V

Ia7.55mA

Vg-30V

Pd11.33W

RL17kΩ

Av23dB

EXECUTIVE SUMMARY

The 100TH is a directly-heated triode from Eimac, introduced around 1938. It provides a gain factor (μ) of 38 with 8400Ω plate resistance. Commonly used in transmitting (set) applications. High-mu Eimac transmitting triode. Needs power drive.

APPLICATIONS

SET outputPush-pull output

Generic triode transmitting (set) stage

• PA/public address

HISTORY

Introduced1938ManufacturerEimac

Pre-War

100TH Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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