1b10-17 Baretter

This type of tube is called "Barretter". A Barretter is a hydrogen-filled glass cylinder into which a thin platinum (iron, tungsten) wire (filament) is placed. Such a device has a nonlinear resistance, which for a slight increase of current in a limited range, results in a significant increase in the voltage on the terminals. The principle of operation is as follows: the applied voltage increases the temperature of the filament and therefore its resistance. As a result, the current in the barretter virtually remains unchanged. Thus, a barretter connected in series with a load keeps current stable as  supplied voltage changes.
Barretters usually can operate at direct and alternating current.

In the notation,  barretter first number refers to the rated current in amperes (1A in this case) while the second two numbers refer to the limits of baretter voltages (10 to 17 Volts).

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Dear Giuseppe,

Many thanks for the useful information on the coding system. Just a quick note to add that the right British name for this device is 'Barretter', whith twin 'r', while in America it is better known as 'Ballast'. Refer to the RCA 'Radiotron Designer's Handbook' and to the many datasheets of similar devices from British manufacturers, as Marconi.

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