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.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

←45

← 421A 45B-EmissionLabs →Compare…

45 Type 45 Triode Vacuum Tube

Triode2.5V / 1.5AUX-4SPICE

SourceRCA datasheetReviewed2026-05-29StatusDataModelCalcModelKoren v1PDF

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

Datasheet ↗SPICE

Type 45 — RCA — triode vacuum tube — (1929)

1.6kΩ

2.2mA/V

4.0pF

7.0pF

3.00pF

GAIN4%

POWER25%

DRIVE98%

LINEARITY95%

SPECIFICATIONS

Heater2.5 V · 1.5 A

Max Plate Voltage275 V

Pa max10 W

Gain Factor4

gm2.175 mA/V

rp1.6 kΩ

Inter-electrode capacitances

Cgk4 pF

Cgp7 pF

Cpk3 pF

PinoutUX-4

Era1929

RarityCollector

HEATER2.5V / 1.5A

MAX PLATE275V / 10W

BASEux4

Source datasheets

6 manufacturer datasheets cross-checked for Type 45

6 verified

TYPICAL OPERATING POINT

SPICE model(2 available)3 .subckt available ↓

Va275V

Ia18.52mA

Vg-63.31V

Pd5.09W

RL4kΩ

Av7.1dB

EXECUTIVE SUMMARY

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.

APPLICATIONS

SET outputPush-pull outputHeadphone output

RCA MI-1356 theatre ampElectro-Voice Circlotron

• Hi-Fi stereo• Headphone amp

HISTORY

Introduced1929ManufacturerRCA

Pre-War

45 Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

CLASSIC CIRCUITS

Single-Ended Triode

45 SE Classic

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 5kΩ

RCA Type 45 Datasheet

SIMILAR TRIODES

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