Jim Thomson wrote:
> Date: Sun, 28 Feb 2010 09:58:56 +0200
> From: "Alex Eban" <alexeban@gmail.com>
> Subject: Re: [Amps] soft start, how to determine if needed?
>
>
> By the way, an old trick that was used in tube type TV sets was to install a
> thermistor in series with the mains. It had a cold resistance of a few tens
> of ohms when cold, dropping to an oh or two after about 20 seconds.
> The only problem was the at switch off you had to remember to let it cool
> before switching on again.
> The Sfernice corporation was manufacturing one type especially for TV sets.
> (about 7W power dissipation) with values ranging from 27 to 1000 ohms.
> Alex 4Z5KS
>
> ## You don't want to install thermistor's in the pri of a plate xfmr, real
> bad news.
>
> ## they have been used in the primary of a FIL xfmr however. The trick is,
> they
> normally run VERY HOT. If they are installed, below the chassis, and
> chassis has
> pressurized air, or any kind of air flow past a thermistor, it will cool the
> thermistor,
> and it's resistance will NOT drop down to an ohm or two. RF Parts sells
> thermistors, rated for step start of FIL xfmr's.
>
In addition, we used to replace those almost as often as the tubes.
Hmmm...I may have given a hint as to how old I am.
73
Roger (K8RI)
> ## what will work, is either a conventional step start, or a ramped up
> triac,take
> your pick.
>
> later... Jim VE7RF
>
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