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Old 5th December 2001, 09:51 AM   #1
diyAudio Member
Join Date: Nov 2001
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?

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.

Thanks in advance.

Luuk Boessenkool

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Old 5th December 2001, 02:58 PM   #2
diyAudio Member
Join Date: Feb 2001
Location: Columbia, SC
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.

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Old 25th January 2009, 07:54 PM   #3
diyAudio Member
Join Date: Dec 2008
Hi Luuk, id strongly recommend you to use 13.3 V for this tubes, i know of the other datasheets but there must be something wrong with them. The PCL works very well with just 12 V (ac or dc) Best regards Thorsten
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