[BC] Current flow in old radios

[nakayle@gmail.com]

This is one reason it's better to use a power transformer and have the
filaments in parallel- then the transformer limits the inrush current.

 -Nat

On 12/4/06, Paul Smith W4KNX <paul at amtower.com> wrote:
> Typical inrush for a tungsten filament is 6X the steady state current,
> unless some other resistance limits the current.
>
> Paul Smith
> W4KNX
> Sarasota, FL
>
> ----- Original Message -----
> From: "Jerry Mathis" <thebeaver32 at gmail.com>
> To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
> Sent: Monday, December 04, 2006 7:46 PM
> Subject: Re: [BC] Current flow in old radios
>
>
> > No, it wasn't deliberate, it was a matter of physics.
> >
> > Tube filaments are somewhat like light bulb filaments; when they are cold
> > their resistance is much lower than when they are at their normal
> operating
> > temperature. The tubes therefore pull more filament current at turn-on
> than
> > they do after they warm up. The tube filaments have more physical mass
> than
> > the light bulb filament, so it takes them longer to warm up. Therefore,
> when
> > the light bulb is already fully lit, the tubes are still drawing larger
> > amounts of current. That current causes a higher voltage than normal
> across
> > the low-voltage light bulb filament, and causes it to glow very brightly
> for
> > about 15 seconds, after which time the tube filaments are near normal
> > operating temperature, and are drawing the normal amount of current.
> >
> > JM
> >
> >
> >
> >
> > On 12/4/06, Kevin Tekel <amstereoexp at yahoo.com> wrote:
> > >
> > > Dave Hultsman wrote:
> > > > The main reason was the reduction of parts.  No power transformer and
> > > > the filaments were series inline including the dial light.  On the
> > > > Hallicrafters AC/DC s-38D receiver the dial light  when you first
> turned
> > > > the set on glowed birghtly for about a half a second until the other
> > > > tubes started to draw current.
> > >
> > > I have an S-38C and its dial light does that.  Maybe it was intentional,
> > > to let people know that the radio is working.  Otherwise if you turn it
> on
> > > and see and hear nothing for 15-20 seconds (not even a pilot light) you
> > > might think it's dead.
> > >
> > > .
> > >
> > > In some other radios where the filaments in series didn't add up to the
> AC
> > > supply voltage, they used a "ballast tube" (a large wire-wound resistor
> > > plugged into a tube base) or even a special resistance line cord to make
> > > up the difference.
> > >
> > >
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