What is the 205D vacuum tube?

The 205D is a triode vacuum tube designed for power (set) applications. WE transmitting triode..

What are the key specifications of the 205D?

Amplification factor μ ≈ 7, transconductance gm ≈ 1.94 mA/V, plate resistance rp ≈ 3.8 kΩ, max plate voltage 400 V, max plate dissipation 14 W, heater 4.5 V / 1.6 A.

Is the 205D still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 205D 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 205D sound like?

WE transmitting 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.

205D Triode Vacuum Tube

Power triode delivering 14W for push-pull and SET designs

TriodeHeater 4.5 V · 1.6 AUX-4Western Electric 1930

Plate dissipation: 14W
Max plate voltage: 400V
Transconductance: 1.94mA/V

205D

Characteristics

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

HeaterDirectly heated

Specifications of 205D — Heater
Heater voltageVh	4.5 V
Heater currentIh	1.6 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 205D — Limiting values
Plate voltageVa max	400 V
Plate dissipationPa max	14 W

Mechanical

Specifications of 205D — Mechanical
Base	UX-4
Rarity	Legendary
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 205D — Small signal
Transconductance	1.94 mA/V
Plate resistance	3.8 kΩ
Amplification factor	7

Capacitances

Specifications of 205D — Capacitances
Grid–cathode	5.2 pF
Grid–plate	4.8 pF
Plate–cathode	3.3 pF

Charactereditorial reading, not a measurement

Specifications of 205D — Character
Gain	7%
Power	35%
Drive	96%
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

Generic triode power (set) stage

Hi-Fi stereo

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : westernelectric.com 205D datasheetActive model : Norman Koren

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 205D1 verified

205D DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: westernelectric.com 205D datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Norman Koren

Context

The 205D is a Western Electric directly-heated triode from the 1930s, closely related to the 300B but with lower power output (around 4-5W in single-ended Class A). It represents an earlier stage in the WE power triode development lineage and is considered by some to have an even more refined midrange than the 300B, with less bass weight but greater delicacy. Like the 101D, it exists in a rarefied collector market where provenance and condition are paramount. Modern reproductions exist from boutique manufacturers, but the tube remains a niche pursuit even within the already specialized DHT community.

History

Introduced: 1930
Manufacturer: Western Electric
Era: Pre-War

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