Home Tubes Asylum

Questions about tubes and gear that glows. FAQ

Current draw with lower filament voltage?


I've read here couple times that filament (or heater, as I have no DHT) current draw under a lower filament voltage is higher.

For this I really can't understand as it runs counter to Ohm's law. Unless the resistance of heater reduces faster than the drop of voltage, otherwise there is no way that current increases with lower voltage. And I can't see any reasons for any feedback mechanisms to cause heater resistance to drop. Well, maybe it will do so slightly as a cooler filament will have slightly lower resistance.

Maybe I misunderstood something? Maybe it does happen to DHT?

But I'll appreciate if anyone can at least confirm my belief that for tubes like 12AX7 or 6SN7 that's indirectly heated, the filament current drops with lower voltage. Or a correction will be good too.


This post is made possible by the generous support of people like you and our sponsors:
  Signature Sound   [ Signature Sound Lounge ]

Topic - Current draw with lower filament voltage? - Ehien 11:39:15 11/21/02 (21)

You can not post to an archived thread.