[R-390] Ballastubes (was inrush current limiters)

[Cecil Acuff]

Ok Guys,

        I agree with you....not that that ever really mattered!  Good site
Jim!

I guess I was trying to get you the correct RMS value before you rectified
it wasn't I!

I was also simplifying things by thinking dividing by 2 in the formula and
rectifying the sinewave was the same...but the .707 formula doesn't ignore
the energy in the other half of the sinewave just because we divided the
full sinewave by 2.

All this aside,  we still didn't solve the ballast tube problem did we!  I
think the bottom line is that you should use what works best for you!  If
you don't mind buying the original 3TF7..it's probably the best solution.
If not there are several good alternate solutions!  Which is great because
we can keep these great radio's going into the future.

I guess in 50 years the focus might be on trying to find a "cheap" fix for
those darned $50 PTO tubes or such!

Life is good!

Merry Christmas to all!

Cecil Acuff


----- Original Message -----
From: Jim Shorney <jshorney@inebraska.com>
To: Cecil Acuff <chacuff@cableone.net>; <R-390@mailman.qth.net>
Sent: Tuesday, December 24, 2002 8:05 PM
Subject: Re: [R-390] Ballastubes (was inrush current limiters)


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>
> On Tue, 24 Dec 2002 19:43:32 -0600, Cecil Acuff wrote:
>
> >        I agree with you Drew.....a half wave rectified sine wave has the
> >same peak value as a the original sine wave....but not the same peak to
peak
> >value.  The peak value of a sine wave is half it's peak to peak value.
You
> >ended up with the peak value by stripping off the top half of the wave
form
> >with the half wave rectifier.  So you have satisfied the first part of
the
> >formula...you divided by 2. Now you multiply by .707 and you have RMS.
>
>
> The output of a half-wave rectifier is not a sine wave - it is a pulse
> waveform with a peak-to-peak value of .5 (one half) the peak-to-peak
> value of the input sine wave.  The .707 formula does not apply to pulse
> waveforms, or any harmonically distorted sine wave for that matter.
> See:
>
> http://www.wodonga.tafe.edu.au/eemo/ne178/tut2_3.htm
>
> About the middle of the page you will see the graphic for half-wave.
> RMS of a half-wave pulse is .5, average is .318, of peak.
>
>
> >The formula in my books say to arrive at the RMS value of a sine wave you
> >divide it's Peak to Peak value by 2 to arrive at Peak value then multiply
> >that Peak value by .707 and you have RMS.
>
>
> This is only true if you are talking about a pure sine wave with no
> harmonic distortion or modulation.  It does not apply to square,
> triangle, pulse, audio, modulated RF or baseband, or any combination of
> the above.  When thinking of the output of a half-wave rectifier, we
> are definitely not thinking of anything close to a pure sine wave.  I'm
> with Drew on this one.
>
>
>
> - --
> Jim Shorney      -->.<--Put complaints in this box
> jshorney@inebraska.com
> nu0c@amsat.org
> Ham Radio NU0C
> Lincoln, NE, USA
> EN10PT
> http://incolor.inetnebr.com/jshorney/
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