What is the 101D vacuum tube?

The 101D is a triode vacuum tube designed for power (set) applications. Earliest WE power triode..

What are the key specifications of the 101D?

Amplification factor μ ≈ 6, transconductance gm ≈ 1.07 mA/V, plate resistance rp ≈ 5.8 kΩ, max plate voltage 190 V, max plate dissipation 2 W, heater 4.5 V / 1 A.

Is the 101D still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 101D as Legendary 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 101D sound like?

Earliest WE power triode.. 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.

101D Triode Vacuum Tube

Low-mu triode with excellent linearity for driver and line stages

TriodeHeater 4.5 V · 1 AUX-4Western Electric 1925

Plate dissipation: 2W
Max plate voltage: 190V
Amplification factor: 6
Transconductance: 1.07mA/V
Plate resistance: 5.8kΩ

101D

Characteristics

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

HeaterDirectly heated

Specifications of 101D — Heater
Heater voltageVh	4.5 V
Heater currentIh	1 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 101D — Limiting values
Plate voltageVa max	190 V
Plate dissipationPa max	2 W

Mechanical

Specifications of 101D — Mechanical
Base	UX-4
Rarity	Legendary
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 101D — Small signal
Transconductance	1.07 mA/V
Plate resistance	5.8 kΩ
Amplification factor	6

Capacitances

Specifications of 101D — Capacitances
Grid–cathode	4.4 pF
Grid–plate	6.4 pF
Plate–cathode	2.9 pF

Charactereditorial reading, not a measurement

Specifications of 101D — Character
Gain	6%
Power	5%
Drive	94%
Linearity	95%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Typical operation

Canonical operating pointModel

B+: 275 V
Load: 13 kΩ
Va: 165 V
Ia: 3.22 mA
Vg: -20 V
Pd: 0.53 W
Gain: 11.6 dB

At Q: Norman Koren
μ: 6.3
gm: 0.75 mA/V
rp: 8.3 kΩ

Design a stage →

Using this tube

Applications

Line stage

Generic triode power (set) stage

Hi-Fi stereoHeadphone amp

Classic circuits

101D SE Classic
Single-Ended Triode0.4W
Western Electric 101D at low-voltage operating point. Rare early telephone repeater triode. Ethereal, delicate sound prized by collectors.
SEVb 135V · Vg -20V · RL 7.5kΩWestern Electric 101D Datasheet

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Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Western Electric 101D datasheet (1941 manual)Active model : Norman Koren

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 101D1 verified

101D DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Western Electric 101D datasheet (1941 manual)
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The 101D is a directly-heated triode from the early Western Electric telephone amplifier lineage, producing roughly 0.5-1W in single-ended Class A. It is prized by a small community of extreme-fidelity enthusiasts who pair it with horn-loaded speakers of 105dB+ sensitivity, finding in it a purity and presence that surpasses even the type 45. The tube requires careful circuit design due to its very low power and high output impedance. Genuine WE 101Ds are museum-grade rarities commanding extraordinary prices, and even reproductions are limited-production specialty items.

History

Introduced: 1925
Manufacturer: Western Electric
Era: Pre-War

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