[Amps] How best to reduce filament voltage?

[Gary Schafer]

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 at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Jim Tonne
> Sent: Friday, February 02, 2007 10:51 AM
> To: Tom W8JI; w2cqm at juno.com; amps at 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 at w8ji.com>
> To: <w2cqm at juno.com>; <amps at contesting.com>; "Norman Hockler"
> <sanorm at 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
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps