Gerald,
Some heaters are quicker than the others that I've seen. One must
remember in indirectly heated cathodes, the heater acts more like a
resistance wire space heater used in ones home than a filament in a bulb
or a directly heated cathode. Your correct, in directly heated, they
heat up right now. In the indirectly heated ones, I've seen them take
several seconds to build up to the bright orange color. Maybe not a full
minute but it took a while. So, the colder heater would draw more
current than the hotter one would. What I'm figuring, you could use a
small enough wire that either the surge would open the wire like a fuse,
or get it hot enough to ruin the insulation. 20 gage wire is pretty
small stuff and I've seen it melt insulation off pretty darn quick in
instances where there was a low ohm short. A lot of the magnet wire
being used now is like Sodereze (low temp insulation). It was designed
so that the heat from a soldering iron will strip the insulation off.
Mostly, all the small rolls of magnet wire you see at electronics
dealers is like this. What I was saying may be over-kill, I'm not sure.
Just from experience with the wire, I just wouldn't run really small
wire for that use.
Will Matney
TexasRF@aol.com wrote:
The filament transformer will limit the current to a large extent.
Also, the resistance of the filament or heater will rise very quickly
when the voltage is applied. For example, the TH347 filament reaches
rated current in just a few milliseconds. I haven't measured the
current of an indirectly heated cathode tube but you can see the color
of the heater turn red almost immediately when voltage is applied,
suggesting that the resistance has increased substantially.
73/k5gw
__________ NOD32 1.880 (20040928) Information __________
This message was checked by NOD32 antivirus system.
http://www.nod32.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|