[ARC5] ART-13 Power Output

[Leslie Smith]

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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