Mullard, Philips Tungsram and possibly Telefunken, shared a common index of valve type designations. As a consequence it is difficult to be certain that a valve with a particular trade mark was not actually made in one of the other factories. This was particularly true with Mullard valves in the UK where some were made by the parent company Philips in the Netherlands.
The type nomemclature for Mullard receiving and amplifying valves and small thyratrons generally consists of two or more letters followed by two or three figures. These symbols provide information concerning the principal uses of the valves, the heater or filament rating, and the type of base, according to the following code.
In some special valves for 'professional' applications the figures follow the first letter and precede the second and subsequent letters.
The first Letter indicates the filament or heater voltage or current:
200 mA Heater
0.5 to 1.5 Volt Filament
6.3 Volt Heater
5.0 Volt Heater
150 mA Heater
2.0 Volt Filament
300 mA Heater
100 mA Heater
The second and subsequent letters indicate the electrode structure:
Voltage Amplifying Pentode
Hexode or Heptode
Heptode or Octode
Electron Beam Indicator. (Magic Eye)
As a third letter only. Secondary Emission Valve See EFP60
Full-Wave Gall Filled Rectifier
The second and third figures are serial numbers indicating a particular design or development. If the first of three figures is a 1 then the base is indicated by the second figure.
The E80F is a professional 6.3 Volt heater audio amplifier pentode on a B9A base.
The ECC83 is a double triode on a B9A base and has a 6.3 Volt heater.
The EF86 is an voltage amplifying pentode, with a B9A base and a 6.3 Volt indirectly heated cathode.
The EL84 is a B9A based output pentode with a 6.3 Volt heater.
The EL34 is an output pentode on an International Octal base and it too has a 6.3 Volt heater.
The EZ80 is a full wave rectifier.
The GZ34 is revealed as being a full wave rectifier on an octal base and is indirectly heated and requires a 5 Volt heater supply.