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can you run a vacuum tube under its rated filament current? Answered

I have a 811a tube and a 3 amp filli. transformer. I know that the 811a runs on 4 amps, but can't I use it with no harmful effects? I know it will run not as well, but will it kill the tube?

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steveastrouk
steveastrouk

Best Answer 11 years ago

Your transformer won't be able to cope, unless you can turn the voltage to the tube down as well.

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electricfan
electricfan

Answer 11 years ago

what do you mean, will the transformer go into saturation, and what do mean by turning down the voltage?

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steveastrouk
steveastrouk

Answer 11 years ago

The transformer will supply 3Amps, it will saturate and be unhappy trying to supply 4A. The only way to match the load to the transformer it to add some load to the filament, so that it only pulls 3A, or tap the transformer so it puts out 3/4 of the voltage.

Your tube won't work right, and you won't damage it under-running it, but your tubes' filament resistance determines the current that it will demand from the supply, not your transformers ability to supply it.

Steve.

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electricfan
electricfan

Answer 11 years ago

Thanks, I've found 2 power packs, one 12v 300milliampa and one 4.8 volt phone charger(330mili). i plan to use a home made step down transformer to bring the voltage down to 6.3 and for the phone charger, i have the phone and the battery gives 6.3 volts so i will rig the charger circuit to the battery to give 6.3 volts. then the amps will add to about 3.95 (.05 won't make a difference right?) by the way i'm using it to make a vttc. also as a back up i have 2 compactatrons (6jm6) if the current is too little. wish me luck

Paul.

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steveastrouk
steveastrouk

Answer 11 years ago

Sounds messy, but it just might work....
Good luck, as you asked ;-)
Steve

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electricfan
electricfan

Answer 11 years ago

i love vacuum tubes, i love there glow, but i hate filiment transformers, there too heavy, or expensive, or most likely both!

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steveastrouk
steveastrouk

Answer 11 years ago

Buy a 6.3 V SMPSU instead then !

Steve

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electricfan
electricfan

Answer 11 years ago

sorry, but whats a smpusu?


paul

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steveastrouk
steveastrouk

Answer 11 years ago

Switched Mode Power Supply - very small for the power rating.