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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Tube Flashing posted by jcmusic on November 7, 2006 at 09:03:34:
The flash you see is caused by the tube heater having low resistance when cold, a prime cause of inrush current. All tubes have this characteristic, even though they don't all visibly flash.Some people like to minimise inrush current by connecting a thermistor, a negative temperature coefficient (NTC) resistor, in series with the power transformer primary. It's usually placed between the on/off switch and the primary winding. Putting it in the primary has the advantage of minimising all inrush, including that due to sudden charging of the smoothing capacitors at switch-on, if you use SS rectifiers.
A thermistor has a high cold resistance and a very low hot resistance, so it works in the opposite way to tube heaters. It's meant to run hot, so it should be kept away from other devices that could be damaged by the heat it generates. It should not be placed on a heat sink, or it won't work properly.
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Follow Ups
- Re: Tube Flashing - Ray Moth 22:44:14 11/08/06 (0)
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