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Bombarding Bore

Pretty "ballzy" trick that over loading of electrical equipment thing you do. I
can see where it would work.  Like a 6 barrel on a carb.

 I use a different method.  You didn't say if you pumped closed stopcock
technique but I assume you do because of the mention of bombing at specific
torr.  My theory is to bombard open stopcock on all units that it is possible
to do that with.  Some 15' and up units require that I start out closed
because of the less resistant path to pumps.  I would rather be continually
drawing off the by products as they are produced.  I match the current / heat
to the tube / electrodes so that the cycle times itself out automatically.  If
I did it right then the tube gets to temperature just before the trodes do so
they finish at approximately the same time.  It is just a matter of matching
the current to the trodes.  I usually start bombarding at as low a pressure as
can be pumped out in the time I put the clips on the electrodes and am ready to
hit the switch.  The other nice thing about this method is that none of the
tube components are over stressed by the bombarding / pumping process.

 I find the area of processing tubes to be a very big problem in the neon
industry.  Very few shops do high enough quality pumping any more.  I am not
sure if this is due to lack of proper training,  misunderstanding of the
principles,  "cheating" the job by reducing fill pressure, improper
calibration of gauges,  or sloppy technique.  But I do know that while I don't
get the original jobs that come into town,  I can count on replacing almost
every tube in the sign within the first year or 2.  I have many, many tubes
that have been operating well over 20 years continuously day and night so
something has to be wrong somewhere. One of the things that I stress to
customers is that neon tubes vary greatly from one source to another. This can
cause a lot of mantainance down the road.  What is called a "hidden cost".

 My pumping system is right off my bending station so that while I am waiting
for a ribbon bend to cool down I pump a tube.  Or I might do another task
while I pump.  Usually,  I find pumping to be the relaxing part of the day.  I
also don't usually have too much problems with breakage even from novice
pumpers due to my glass technique.  The installers call it " iron glass ". 
They appreciate it when they are 40 floors up in the wind and stressing out a
double back going into a housing they can't reach.  I learned to bend strong
glass because a lot of work is last minute and can't be repaired in enought
time.  It has to be right the first time.  I also charge for it.  I've had
people want to pay less because it doesn't have to be perfect.  I tell them it
takes just as long to heat the glass and bend it wrong as it does to bend it
right.

 I talked to someone the other day that told me of a technique some shops use
to prevent flash back to the pumps.  They put wires at a specific distance
apart between the insulators on the secondary so that as the resistance of the
tube approaches critical,  it will take the path across the air gap between
the bombarder secondary.  It could be adjusted so it was just the right
distance and could save stopcocks,  guages,  and who knows what else.  A new
one on me but I thought it was a good idea.  They use the same technique on
power line transformers to shunt high voltage surges to ground and away from
the transformer.  I saw a sparrow get fried once when he stepped across the
gap.  He went BANG!

  E-mail from: Tom Biebel, 02-Sep-1995