Questions about tubes and gear that glows. FAQ
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.
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Topic - Current draw with lower filament voltage? - Ehien 11:39:15 11/21/02 (21)
- Positive temperature coefficient of Tungsten. - Mark Kelly 14:52:08 11/21/02 (20)
- Re: Positive temperature coefficient of Tungsten. - Ehien 15:58:30 11/21/02 (19)
- Cold resistances - Mark Kelly 18:47:39 11/21/02 (12)
- Re: Cold resistances (pretty much confirmed) - Steve O 22:30:35 11/21/02 (9)
- "Sovteks meas about twice the cold resistance of the US brands - JJ Analog 22:42:04 11/21/02 (8)
- Lower Purity W: Good? Bad? Neither? - Steve O 23:08:26 11/21/02 (6)
- Re: Lower Purity W: Good? Bad? Neither? - Ehien 23:15:36 11/21/02 (5)
- some more cold resistance - Ehien 23:08:08 11/21/02 (0)
- Re: Cold resistances - Ehien 21:35:09 11/21/02 (1)
- Much less than 2 seconds - Mark Kelly 20:01:47 11/22/02 (0)
- Re: Positive temperature coefficient of Tungsten. - klaus 17:06:08 11/21/02 (5)
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