[ARC5] ART-13 Power Output

Thu Nov 26 17:45:19 EST 2015

  Hello Jeep,
  All this proves that Richard Feynman was correct on two points.
  First, it's necessary to "do the experiment", and after that to
  understand that "nature cannot be fooled".

  I like to hear the experience of others, because it broadens my
  understanding.

  Now I'm less confident about the idea of running (receiver) filaments
  5% under-voltage.
  I found supporting evidence for this in a (very old) technical book I
  once saw.
  According to that source, dropping the filament voltage to an
  incandescent light would double the life of the globe - but give less
  light out.  Since the eye was logarithmic (in response) the decrease
  in apparent brightness was less of a problem that the benefit of
  longer tube life.   Putting this in the context of a recent memory of
  depression and the uncertainty of when WWII might end, I can
  understand why the ARRL published this info.

  73 de Les Smith
  vk2bcu at operamail.com

On Fri, Nov 27, 2015, at 01:13, DSP3 wrote:
> Les,
> 
> Well, you're arguably correct on all fronts.  I elected to simply boost 
> the a.c. input to the entire power supply, the results noted in the 
> original post.  I then split out the DC filament supply and ran it up to 
> 28v.  The power did come up to about 60% of the previous increase.  What 
> also did occur, however, was that the drive level was now up in the 
> normal area.  So, looks like they all have a factor.  I do believe that 
> my filament voltage may have been lower that I thought... maybe as low 
> as 25v?  That would account for the noteworthy increase.  In that I use 
> the ART-13s only a couple of hours a week, at most, running a 
> conservative voltage probably won't do much for me.  I do set the 
> voltage on the 3-500Zs in the amplifiers I use at 5% less and limit the 
> inrush.  I appreciated your comments....
> 
> Jeep - K3HVG
> 
> 
> 
> On 11/25/2015 5:29 PM, Leslie Smith wrote:
> > G'day Jeep!
> > Recently I was asked to look at a non-functioning piece of laboratory
> > equipment - Bragg's Apparatus.
> > The key point of failure was the x-ray generator tube.  I forget the
> > detail of the tube, but from memory the filament circuit had been
> > faulty.  A fellow I know, Ken, had re-built the filament supply, and
> > from memory set the filament current,  using a current regulator circuit
> > to deliver the current - to spec.  Ken is a precise fellow and set the
> > current "right on spec" - if such a thing is possible.  If my memory is
> > good "spec" was 1.25A, but my memory may be faulty on that point.
> >
> > No problem could be found.  Everything was as it should be.   A second
> > tube did nothing.  Then I wound the current "up" ever so-slightly over
> > 1.25A.   Bingo!   Mr. Bragg was measuring x-ray diffraction again.  I
> > was surprised that such a small (over-spec) adjustment of filament
> > current make the difference between nothing and working as expected.
> >
> > Now, an x-ray tube is quite different from the tubes in your set up.
> > Also, I remember that 'tubes' running with -5% filament voltage lasted a
> > LOT longer.  (My recollection is that this was in the ARRL hand-book,
> > certainly early WWII.  As a kid, I thought this was very important and
> > even calculated the value of a resistor that would do this
> > "preservation" for me.)  So I and both surprised and not surprised by
> > your observation.
> >
> > I make one further observation.  The B+ supply increased by a factor of
> > 1.15 and power is related to the square of the voltage.  1.15^2 x 110 ->
> > 145, and that's not too far below your measured 150W (probably within
> > the limit of error of your power meter etc).  It may be that you have
> > measured an increase in power due to increased B+ supply.  That's
> > another point of view.
> >
> >    73 de Les
> >    vk2bcu at operamail.com
> >    (end)
> >
> > On Thu, Nov 26, 2015, at 08:30, DSP3 wrote:
> >> Not to re-open a closed discussion but I noticed that one (probably
> >> both) of my ARC-8 setups had apparently dropped in power output.  The
> >> p.s. for this system has the filament voltage at about 26.5 volts.  With
> >> the line voltage down a bit as a function of increased neighborhood
> >> usage (assumed), the ART-13 was putting out about 110 watts.  I noticed
> >> that the LV reading was down at the bottom of the arc, as was the
> >> drive.  So, I put a 20A variac in the line and bumped the line voltage
> >> up so that I got 28v on the filaments.  The low B+ came up from 380v to
> >> about 410v and the B+ from 1000v up to about 1150v.  The power out is
> >> now back to an easy 150 watts, which I re-tuned back to a nominal 125
> >> watts.  It would appear that filament voltage is more of a factor that I
> >> previously appreciated.  As I mentioned earlier, I use about 700pf of
> >> loading on 75 meters.  Anyway, as Chief Inspector Clouseau would say...
> >> "I have sol-ved the case".....
> >>
> >> Jeep - K3HVG
> >>
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