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

[Jim Shorney]

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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
jshorney@inebraska.com
nu0c@amsat.org
Ham Radio NU0C
Lincoln, NE, USA
EN10PT
http://incolor.inetnebr.com/jshorney/
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