I wonder if anyone has ever tried negative temperate coefficient thermistors to
do a step start. They have are available in a range of values but a thermistor
that has a 10 ohm cold resistance would have a final resistance after 30
seconds of ~.3 ohms.
A curve for such a device is at http://www.joyin.com/image/itcurve.gif.
These are commonly used in switch mode power supplies where there would be a
hugh inrush of current to charge the input caps when power is first applied.
The advantages of this sort of thing is that they are small and can be put
anywhere near the input to the filament transformer (they do get hot though)
and there are no moving parts or contacts to worry about.
The disadvantage is that there is some residual resistance that stays in the
circuit all the time. If this sort of device had to be placed at the input to a
1KW (average) amplifier that didn't have separate plate and filament
transformers (operated on 120VAC) primaries there would be about a 2% droup. I
don't know if that's significant in the big picture.
- Bill
On Jun 9, 9:47am, measures wrote:
> Subject: Re: [AMPS] Step-start. questiobn DE K0FF
>
> >
> >In the module that Alan Harbach makes, he uses 20 ohm resistors for 220
> >volts and 10 ohm resistors for 120 volts.
> >
> With the right circuit, one value of R is optimal for dual-voltage
> amplifiers. See circuit on my web site. // For legal limit amps, 2,
> 20-ohm resistors are about right. When the amp is switched to 120v, the
> two, 20-ohm resistors act like one 10-ohm resistor.
>
> cheers, Mike
>
> >----- Original Message -----
> >From: "K0FF" <K0FF@ARRL.NET>
> >To: "Amps" <amps@contesting.com>
> >Sent: Friday, June 09, 2000 9:57 AM
> >Subject: [AMPS] Step-start. questiobn DE K0FF
> >
> >
> >|
> >| I have an SB221 on 110VAC (for portable/motel ops) and want to install a
> >| step-start. I already have a nice 110 VAC relay, but don't know the
> >correct
> >| size of series resistors to use. Any ideas?
> >|
> >| George, K0FF
> >|
> >|
> >| --
> >| FAQ on WWW: http://www.contesting.com/FAQ/amps
> >| Submissions: amps@contesting.com
> >| Administrative requests: amps-REQUEST@contesting.com
> >| Problems: owner-amps@contesting.com
> >|
> >
> >
> >--
> >FAQ on WWW: http://www.contesting.com/FAQ/amps
> >Submissions: amps@contesting.com
> >Administrative requests: amps-REQUEST@contesting.com
> >Problems: owner-amps@contesting.com
> >
> >
>
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
>
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
> Submissions: amps@contesting.com
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> Problems: owner-amps@contesting.com
>
>-- End of excerpt from measures
--
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