The transformer in question is a power transformer not just a filament
transformer. It also supplies the high voltage.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jim Tonne
> Sent: Friday, February 02, 2007 10:51 AM
> To: Tom W8JI; w2cqm@juno.com; amps@contesting.com; Norman Hockler
> Subject: Re: [Amps] How best to reduce filament voltage?
>
>
> Tom wrote:
>
> > This will not work. Don't do it.
>
> in reply to
>
> >> Install a resistor on the primary side of the transformer.
>
> which is what I would have suggested.
>
> > It will totally hose the voltage regulation under load,
>
> The load is constant so "regulation" in the usual sense
> (same output voltage with varying load value) is not an
> issue. A series resistance would limit inrush. A series
> resistance at the transformer primary would limit inrush
> to the transformer as well.
>
> > the resistors would have to be huge.
>
> Seems to me the resistor WATTAGE value would be
> the same regardless of whether it was in the primary or
> the secondary of the filament transformer.
>
> Another way around this whole issue is to use a
> relatively small bucking voltage (obtained from, say,
> a filament transformer) in series with the transformer
> primary to reduce its input voltage. That would of
> course be very efficient. By putting a variac or
> equivalent on the primary of the buck transformer
> the filament voltage could be tweaked to perfection.
>
> - JimT
>
>
>
>
> ----- Original Message -----
> From: "Tom W8JI" <w8ji@w8ji.com>
> To: <w2cqm@juno.com>; <amps@contesting.com>; "Norman Hockler"
> <sanorm@columbus.rr.com>
> Sent: Friday, February 02, 2007 10:32 AM
> Subject: Re: [Amps] How best to reduce filament voltage?
>
>
> > This will not work. Don't do it.
> >
> >> Install a resistor on the primary side of the transformer.
> >> Much
> >> lower current and the resistors will act as a
> >> soft start for the filament to damp the inrush when you
> >> first turn on
> >> power. Set the resistor value with the
> >> tube on and warm There are many sliding tap resistors
> >> available from
> >> the distributors or a fixed one will
> >> work as well. Ohms law calculation to determine the value.
> >
> > It will totally hose the voltage regulation under load, and
> > the resistors would have to be huge.
> >
> > 73 Tom
>
>
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