What is the 10Y vacuum tube?

The 10Y (10Y / VT-25) is a triode vacuum tube designed for power (set) applications. Legendary DHT. Ethereal midrange clarity..

What is a 10Y substitute or equivalent?

Direct equivalents to the 10Y include VT-25, UX-210, 801A. 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 10Y?

Amplification factor μ ≈ 8, transconductance gm ≈ 1.5 mA/V, plate resistance rp ≈ 5.3 kΩ, max plate voltage 450 V, max plate dissipation 15 W, heater 7.5 V / 1.25 A.

Is the 10Y still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 10Y as Collector 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 10Y sound like?

Legendary DHT. Ethereal midrange clarity.. 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.

10Y VT-25 Triode Vacuum Tube

Also known as VT-25 · UX-210 · 801A

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

TriodeHeater 7.5 V · 1.25 AUX-4RCA·GE·Sylvania 1927

Plate dissipation: 15W
Max plate voltage: 450V
Transconductance: 1.5mA/V

10Y

Characteristics

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

HeaterDirectly heated

Specifications of 10Y — Heater
Heater voltageVh	7.5 V
Heater currentIh	1.25 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 10Y — Limiting values
Plate voltageVa max	450 V
Plate dissipationPa max	15 W

Mechanical

Specifications of 10Y — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 10Y — Small signal
Transconductance	1.5 mA/V
Plate resistance	5.3 kΩ
Amplification factor	8

Capacitances

Specifications of 10Y — Capacitances
Grid–cathode	4 pF
Grid–plate	7 pF
Plate–cathode	3 pF

Charactereditorial reading, not a measurement

Specifications of 10Y — Character
Gain	8%
Power	38%
Drive	95%
Linearity	95%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	Va	Vg1 / Rk	Ia	Source
triode connection, single-endedclass not stated · fixed bias	250 V	-95 V	45 mA	OCR, to be checked RCA · 1946 · p. 1 · transcript

Using this tube

No interactive loadline model for this tube yet — download a SPICE model below to simulate it in LTspice or ngspice.

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, 2026

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 10Y / VT-251 verified

10Y DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·GE·Sylvania
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The 10Y is a directly-heated triode from RCA·GE·Sylvania, introduced around 1927. It provides a gain factor (μ) of 8 with 5300Ω plate resistance. Commonly used in power (set) applications. Legendary DHT. Ethereal midrange clarity.

History

Introduced: 1927
Manufacturer: RCA·GE·Sylvania
Era: Pre-War

METRIX TESTER