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Old 1st February 2013, 04:12 PM   #1
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Default testing voltage on tube filament, without the tube

I would like to adjust the tube heater voltage without using the tube. The tube rating is 5V/2A. I believe I can use a resistor in its place with the same effect, but I have never tried. Can someone confirm what should be the resistor's resistance and power rating? And if this is a good method?

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Old 1st February 2013, 04:25 PM   #2
kevinkr is offline kevinkr  United States
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Yes, this is a good technique. Use ohms law to calculate the required resistance and power..

At least double the rated power of the resistor based on calculation.

R = E/I where E is the operating voltage and I is the desired current.

P = I x E
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Old 1st February 2013, 04:33 PM   #3
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Thanks for the fast reply.
So for the 5V/2A tube it would be a 2.5ohm resistor rated at 20W, that's it?
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Old 1st February 2013, 05:33 PM   #4
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Yes, OK, but use a higher wattage resistor, because it may run hot. Also, if the 5V is from a rectifier, be aware with the high voltages at their anodes.

Good luck.
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Old 1st February 2013, 06:00 PM   #5
JMFahey is offline JMFahey  Argentina
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I would like to adjust the tube heater voltage without using the tube.
Just curious, haw are you going to "adjust the tube heater voltage"?
Where's such voltage coming from?
Is it a rectifier tube?
Does it have HV applied to it?
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