[ARC5] ART-13 Power Output

[DSP3]

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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