What is the 45 vacuum tube?

The 45 (Type 45) is a triode vacuum tube designed for power (set) applications. Purest SET tone..

What is a 45 substitute or equivalent?

Direct equivalents to the 45 include 245, VT-52. 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 45?

Amplification factor μ ≈ 4, transconductance gm ≈ 2.175 mA/V, plate resistance rp ≈ 1.6 kΩ, max plate voltage 275 V, max plate dissipation 10 W, heater 2.5 V / 1.5 A.

Is the 45 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 45 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 45 sound like?

Purest SET tone.. 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.

45 Type 45 Triode Vacuum Tube

Also known as 245 · VT-52

High-power directly-heated triode for single-ended amplification

TriodeHeater 2.5 V · 1.5 AUX-4RCA 1929

Plate dissipation: 10W
Max plate voltage: 275V
Transconductance: 2.175mA/V

Characteristics

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

HeaterDirectly heated

Specifications of 45 — Heater
Heater voltageVh	2.5 V
Heater currentIh	1.5 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 45 — Limiting values
Plate voltageVa max	275 V
Plate dissipationPa max	10 W

Mechanical

Specifications of 45 — Mechanical
Base	UX-4
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 45 — Small signal
Transconductance	2.175 mA/V
Plate resistance	1.6 kΩ
Amplification factor	4

Capacitances

Specifications of 45 — Capacitances
Grid–cathode	4 pF
Grid–plate	7 pF
Plate–cathode	3 pF

Charactereditorial reading, not a measurement

Specifications of 45 — Character
Gain	4%
Power	25%
Drive	98%
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

RCA MI-1356 theatre ampElectro-Voice Circlotron

Hi-Fi stereoHeadphone amp

Classic circuits

45 SE Classic
Single-Ended Triode2W
The type 45 at its recommended operating point. Delicate and refined with a purity that few tubes can match. The audiophile's secret weapon.
SEVb 250V · Vg -50V · RL 5kΩRCA Type 45 Datasheet

Replace or compare

Sources

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

Manufacturer datasheets

6 manufacturer datasheets cross-checked for Type 456 verified

45 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The type 45 is a directly-heated triode from the late 1920s, producing roughly 1.5-2W in single-ended Class A. It is widely regarded as possessing the most transparent, pure midrange of any power tube ever made, with a directness that makes 300Bs sound colored by comparison. The penalty is its extremely low power output, demanding speakers of 97dB+ sensitivity. Its 2.5V filament supply and fragile construction make it a tube for dedicated enthusiasts, with NOS RCA, Sylvania, and United Electronics examples being the most prized.

History

Introduced: 1929
Manufacturer: RCA
Era: Pre-War

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