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

Mon, 23 Dec 2002 21:58:34 -0600

Greetings all,

        Here is how I remember it from my school days....RMS = Peak V X .707

An AC waveform is a Peak to Peak waveform.  Moving equal amounts above and
below Zero.  (in this case)

You arrived at peak value by half wave rectifying the Peak to Peak sine
wave.  You now multiply that value by .707 to get the RMS value.  To go from
RMS back to Peak you multiply by 1.414 and then double that to get Peak to
Peak values.

I verified that in a radio engineering handbook.  (it's been a while since I
used this stuff too)

Cecil Acuff

----- Original Message -----
From: Jim Shorney <[email protected]>
To: <[email protected]>; Drew Papanek <[email protected]>
Sent: Monday, December 23, 2002 8:30 PM
Subject: Re: [R-390] Ballastubes (was inrush current limiters)

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> On Mon, 23 Dec 2002 17:37:02 -0500, Drew Papanek wrote:
>
>
> >RMS voltage and current are what define heating power in a waveform (DC
> >"waveform" included).
>
> That's what I thought, but all the references I could find searching
> last night only talked about average.
>
>
> >One of my references lists RMS value of a half wave rectified sinewave to
be
> >half the PEAK value.
>
>
> I finally found a reference that agrees with this.
>
>
>
> >The half
> >wave rectified RMS value:  ( 35.6)(.5)=17.8 VRMS.
>
>
> I knew there was a reason this idea still bothered me....
>
>
>
> >A 12AU7 will not work as it
> >draws 150 mA when configured for 12 volts.
>
>
> Thought so, but I was focused in on the other area.
>
>
> >Replacing the BallasTube with solid state current regulator has also been
> >discussed.   A while back Dr. Jerry designed an AC current regulator
using a
> >full wave bridge wrapped around an LM317 configured as a DC current
> >regulator, providing a clipped sine wave
>
>
> This is exactly one of the ideas I was kicking around, since I have a
> drawer full of 317Ts.
>
>
> >As far as regulator-induced noise is concerned, filtering would help but
I
> >am not sure that this is necessary.
>
>
> Manufacturer's recommended filter/bypass caps are always necessary,
> IMHO.  I remember the time a CBer brought me a home-built 12v power
> supply that would spike to >18 volts when he unkeyed his radio.  The
> solution was to get out the data book and install the caps for the 317T
> that National Semi said shouldbe there for stability and transient
> response.  There was also the blurb in QST years ago from the ham who
> tossed a bunch of bypass caps at the regulators and zeners in, IIRC, a
> TR7 and IC551 and saw a noticable improvement in the noise floor.
>
>
> >Another solid state regulator approach is to half wave rectify the
25.2VAC,
> >filter and apply to a 3 terminal regulator configured as a 300 mA DC
> >regulator.
>
>
> The same without filtering should give a clipped half-sine wave as
> above.  Since we start out with an RMS of 17.8 volts, there should be
> enough headroom.  Another variation I've been thinking about.
>
>
> >I believe that the imbalance is small compared to the total transformer
load
> >and probably wouldn't make much difference.
>
>
> I tend to agree.
>
>
> >Have a happy holiday and may Santa bring each of you a sleighload of
3TF7's!
>
>
> Maybe I should shut up until I actually get my radio up and running.
> Or at least find out if my 3TF7 is good...
>
> God rest ye merry, gentlemen.
>
> - --
> Jim Shorney      -->.<--Put complaints in this box
> [email protected]
> [email protected]
> Ham Radio NU0C
> Lincoln, NE, USA
> EN10PT
> http://incolor.inetnebr.com/jshorney/
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