On 8/7/24 22:22, Robin Szemeti via Emc-users wrote:
No colour TV's use an NTC in the degauss .. they use a PTC. As the device
heats up, the resistance goes up and the current drops ...
That would also work, but I've had multiple failures of the device in a
past life fixing tv's. A couple even burned up the coil. That was from
the first color tv's to about '62 when I got a 1st phone & a job at a tv
station. I spent the rest of my working life till 67 yo keeping them on
the air.
We have sold literally tens of thousands of high power, transformer driven
audio amplifiers (multi-kilowatt) with a pair of NTC's in the startup
circuit, with no significant issues. Obviously in a transformer design,
they are in the primary not the secondary, but an NTC would work fine in
the output of the rectifier ... but actually, what we do on later switch
mode usits is to use a PTC after the rectifier ... which sounds weird ...
the idea is it forms a startup resistance which is shorted out with a relay
once working voltage is reached ... but in the even of a fault at startup,
it just gets hot, goes high resistance and sits their quietly cooking, the
voltage on the caps never rises due to the fault, and the relay never
closes, saves a lot of blown tracks!
Neat!
Something HP never learned. They never learned about curie temps in
ferrite either.
[...]
Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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