What is the Siemens-Bi vacuum tube?

The Siemens-Bi (Siemens Bi / PTT100) is a pentode vacuum tube designed for industrial / power applications. Rare Siemens industrial pentode..

What is a Siemens-Bi substitute or equivalent?

Direct equivalents to the Siemens-Bi include None. 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 Siemens-Bi?

Transconductance gm ≈ 15 mA/V, max plate voltage 300 V, max plate dissipation 12 W, heater 6.3 V / 0.9 A.

Is the Siemens-Bi still in production?

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

Rare Siemens industrial pentode.. 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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Siemens-Bi Siemens Bi / PTT100 Pentode Vacuum Tube

Pentode6.3V / 0.9A9-pin Noval

SourceSiemensReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Power pentode delivering up to 12W in pentode, UL, or triode mode

Datasheet ↗

Siemens Bi / PTT100 — Siemens — pentode vacuum tube — (1958)

15.0mA/V

10.0pF

0.8pF

8.00pF

GAIN0%

POWER30%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 0.9 A

Max Plate Voltage300 V

Pa max12 W

Gain Factor—

gm15 mA/V

rp—

Inter-electrode capacitances

Cgk10 pF

Cgp0.8 pF

Cpk8 pF

Pinout9-pin Noval

Era1958

RarityCollector

HEATER6.3V / 0.9A

MAX PLATE300V / 12W

BASEnoval

EXECUTIVE SUMMARY

The Siemens-Bi is a indirectly-heated pentode from Siemens, introduced around 1958. Commonly used in industrial / power applications. Rare Siemens industrial pentode.

APPLICATIONS

Power output

Generic pentode industrial / power stage

HISTORY

Introduced1958ManufacturerSiemens

Golden Age

Siemens-Bi Datasheet

Frank's Electron Tube Pages · PDF

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METRIX TESTER

Test this tube on a Metrix

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

SIMILAR PENTODES

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