The type number consists of a number followed by a capital letter, a figure and in some cases by a second capital letter (e.g. 85A2, 150C1K).

Number (average burning voltage in volts)

First letter (current range)

A - max. 10 mA
B - max. 22mA
C - max. 40mA
D - max. 100mA
E - max. 200 mA

Figure (serial number)

Second letter (tube base)

E - Edison
K - Octal 8-pin base
P - P-base

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