What is the UY85 vacuum tube?

The UY85 (UY85 / 38A3) is a rectifier vacuum tube designed for rectifier applications. Series-heater half-wave rectifier..

What is a UY85 substitute or equivalent?

Direct equivalents to the UY85 include 38A3, U381. 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.

Is the UY85 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the UY85 as Common 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 UY85 sound like?

Series-heater half-wave rectifier.. 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

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UY85 UY85 / 38A3 Rectifier Vacuum Tube

Rectifier38V / 0.1A9-pin Noval

SourceMullard·PhilipsReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Full-wave rectifier for vacuum tube power supply designs

Datasheet ↗

UY85 / 38A3 — Mullard·Philips — rectifier vacuum tube — (1955)

4.0pF

5.0pF

3.50pF

GAIN0%

POWER0%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater38 V · 0.1 A

Max Plate Voltage250 V

Pa max—

Gain Factor—

gm—

rp—

Inter-electrode capacitances

Cgk4 pF

Cgp5 pF

Cpk3.5 pF

Pinout9-pin Noval

Era1955

RarityCommon

HEATER38V / 0.1A

MAX PLATE250V

BASEnoval

Source datasheets

6 manufacturer datasheets cross-checked for UY85 / 38A3

6 verified

EXECUTIVE SUMMARY

The UY85 is a indirectly-heated rectifier from Mullard·Philips, introduced around 1955. Commonly used in rectifier applications. Series-heater half-wave rectifier.

APPLICATIONS

Power supply rectification

Generic rectifier rectifier stage

HISTORY

Introduced1955ManufacturerMullard·Philips

Golden Age

UY85 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

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