Xref: utzoo sci.electronics:4116 rec.photo:3539
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!think!ames!eos!jbm
From: jbm@eos.UUCP (Jeffrey Mulligan)
Newsgroups: sci.electronics,rec.photo
Subject: Re: Xenon flash tube sources
Message-ID: <1774@eos.UUCP>
Date: 21 Oct 88 00:21:08 GMT
References: <944@ritcv.UUCP>
Organization: NASA Ames Research Center, California
Lines: 55

From article <944@ritcv.UUCP>, by cep4478@ritcv.UUCP (Christopher E. Piggott):

> 		(1) RADIO SHACK:
> 			Part number 272-1145 - $3.95/ea
> 			Trigger: 4Kv, Anode: 200-300v
> 			(with a data sheet, but not amazingly helpful)

> 	I don't know how to use either of these tubes!!!  I posted to
> sci.electronics last month about how to make use of them with a 12vdc power
> source, and got *NO RESPONSES*.  If you can help me, get in touch by mail
> (preferrably bitnet, as it's more reliable).  Thanks, and good luck, Steve.

In my college days I did a lot of playing around with the
R.S. tubes.  I was using a power supply of around 160V dc
(This was just the 115V ac run through an isolation transformer
and rectified).  The flash capacitor was a big thing, a couple
of microfarads rated for 400V.  A prof. put me onto a cute
trick to get them to recharge to double the supply voltage:
they recharged through a series diode/inductor.  The inductor
kept the recharging current low until the gas had de-ionized,
while the diode kept the flash capacitor from discharging back
onto the supply capacitors.  The charging curve looked like
a half cycle of a sine wave.

Radio Shack also sells the little trigger transformer for these
guys.  I used an SCR to discharge a small capacitor through the
primary to get the kV needed to ionize the xenon.  My memory
is a little hazy here, but I think I needed a transistor to
inject enough current to trigger the SCR from ttl control signals.
I also used opto-isolators between the high voltage stuff and
the logic circuitry.

Things were great until I started trying to get the things to strobe
at 1kHz (don't ask why).  I ended up making my own inductors
to get the right L value for a 1 ms recharging time.  Unfortunately,
the inductors I made (magnet wire wound onto a half inch steel rod)
had too much resistance (a few hundred ohms), resulting in a non-neglible
charging current at the end of the flash.  What happened was that
these babies would strobe at 1kHz for a few seconds at which
point they turned into arc lamps- i.e. the gas just stayed ionized
and shorted out the power supply.  At this point they were HOT!

The moral was I wasted a lot of effort designing a fancy system
around a $3 flash tube for which I had no data sheets and couldn't
perform in the way I wanted it to.  I have a nice catalog from
EG&G describing their line of flashtubes, they do give specs,
but of course their stuff is expensive.  Impressive stuff, though,
like the 4 ft. water cooled flashtube used for aerial phtography...


-- 

	Jeff Mulligan (jbm@aurora.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-6290