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 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.

Siemens-Bi Siemens Bi / PTT100 Pentode Vacuum Tube

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

PentodeHeater 6.3 V · 0.9 A9-pin NovalSiemens 1958

Plate dissipation: 12W
Max plate voltage: 300V
Transconductance: 15mA/V

Siemens-Bi

Characteristics

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

HeaterIndirectly heated

Specifications of Siemens-Bi — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.9 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of Siemens-Bi — Limiting values
Plate voltageVa max	300 V
Plate dissipationPa max	12 W

Mechanical

Specifications of Siemens-Bi — Mechanical
Base	9-pin Noval
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of Siemens-Bi — Small signal
Transconductance	15 mA/V

Capacitances

Specifications of Siemens-Bi — Capacitances
Input	10 pF
Grid–plate	0.8 pF
Output	8 pF

Charactereditorial reading, not a measurement

Specifications of Siemens-Bi — Character
Gain	0%
Power	30%
Drive	50%
Linearity	75%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

Power output

Generic pentode industrial / power stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

Siemens-Bi DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Siemens
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

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

History

Introduced: 1958
Manufacturer: Siemens
Era: Golden Age

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