What is the D3A vacuum tube?

The D3A (D3a) is a pentode vacuum tube designed for preamp / driver applications. German Postamt legend..

What is a D3A substitute or equivalent?

Direct equivalents to the D3A include 7721. 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 D3A?

Amplification factor μ ≈ 80, transconductance gm ≈ 35 mA/V, plate resistance rp ≈ 120.0 kΩ, max plate voltage 220 V, max plate dissipation 4.2 W, heater 6.3 V / 0.315 A.

Is the D3A still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the D3A as Sought-after 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 D3A sound like?

German Postamt legend.. 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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D3A D3a Pentode Vacuum Tube

Pentode6.3V / 0.315A9-pin NovalSPICE

SourceSiemens D3a/7721 datasheet (pearl-hifi mirror)Reviewed2026-05-29StatusDataModelCalcModelAyumi NakabayashiPDF

Small-signal pentode for low-noise voltage amplification

Datasheet ↗SPICE

D3a — Siemens·Telefunken — pentode vacuum tube — (1958)

120.0kΩ

35.0mA/V

10.0pF

0.0pF

2.10pF

GAIN80%

POWER11%

DRIVE0%

LINEARITY60%

SPECIFICATIONS

Heater6.3 V · 0.315 A

Max Plate Voltage220 V

Pa max4.2 W

Gain Factor80

gm35 mA/V

rp120.0 kΩ

Inter-electrode capacitances

Cgk10 pF

Cgp0.035 pF

Cpk2.1 pF

Pinout9-pin Noval

Era1958

RaritySought-after

HEATER6.3V / 0.315A

MAX PLATE220V / 4.2W

BASEnoval

Source datasheets

3 manufacturer datasheets cross-checked for D3a

3 verified

TYPICAL OPERATING POINT

Va105V

Ia13.86mA

Vg-1V

Pd1.45W

RL240kΩ

Av38dB

EXECUTIVE SUMMARY

The D3A is a indirectly-heated pentode from Siemens·Telefunken, introduced around 1958. It provides a gain factor (μ) of 80 with 120.0kΩ plate resistance. Commonly used in preamp / driver applications. German Postamt legend.

APPLICATIONS

Voltage amplifier

Generic pentode preamp / driver stage

HISTORY

Introduced1958ManufacturerSiemens·Telefunken

Golden Age

D3A Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

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