• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Filament for the PCL86

How do I construct a filament for the PCL86?

I do not understand how to implement the filament for a tube that depends on a steady current for heating the tube.

The questions that I have:
1 - Is it essential that the given current is used? (In this case 300mA)?
2 - The Uf seems to be less critical, is this correct?
3 - What kind of methods can I use?
4 - I am planning on using it in a pre-amplifier, should I use AC or DC for heating the tube?

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Known data:
Uf - somewhere between 13.3V and 14.5V (depending on which datasheet you use)
If - 300mA

I do have a transformer with 12V-AC on the secondary side.
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Thanks in advance.

Luuk Boessenkool
 
Luuk,
1-2) It's a good idea to come pretty close to the rated current. There's a curve showing the lifetime (cathode emissions) of a tube at different filament voltages. It falls off pretty rapidly on either side of the rated voltage. If you're not sure of the exact voltage you need, use a variac and bring the voltage up slowly until you see the proper current flowing through the filament. Measure the voltage.
Some people say that the best way to run a tube is with a current source set to the proper current. That way the voltage can be whatever it needs to be.
3) If you mean methods for a filament supply, you don't need anything fancy. If you want to run AC on your filaments, just come from the filament winding. If you want DC, then transformer->rectifier->cap->regulator will do the trick.
4) For preamps, I'd use DC.

Grey