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Logandiana
Tinkerer
Username: Logandiana
Post Number: 7
Registered: 04-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 01, 2010 - 12:37 pm: | 
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So at a garage sale recently I found a few old flashes in various conditions. A couple are sunpaks, and a couple are something else which I have never heard of. Upon inspecting them they seem to be in good condition. One of them is in perfect condition except that the bulb itself appears to be burned out. I plan to open it up and replace the bulb but I am wondering about what size/value is correct. Obviously I can’t install a flash bulb that would fit in a studio light and obviously I can’t install one that would fit in a pop up flash of a point and shoot. My question is: Is there any way to know what size flash tube would work, based on a voltage reading or from the size of the batteries used, etc? I guess a better way to ask is, are flash tubes labeled in such a way that you would be able to interchange them based on their value? (like the same way batteries are labeled, If I know a device takes 6volts then it shouldn’t matter if I have 4AA batteries or 2 3volt batteries or some other combination, as long as I have 6volts).
I guess, the reason that I am asking is that I may have a possible source for a bunch of new old stock flash tubes. I should be able to do some flash surgery to get a new one in there, but I don’t want to put one that is too small and end up blowing it up , but I also don’t want to put one in there that is too big and have it be underpowered.
I hope this post makes sense. |
Leesobing
Tinkerer
Username: Leesobing
Post Number: 61
Registered: 01-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 01, 2010 - 08:24 pm: |
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Dear Logandiana,
I would share my experiences.
Most of time Flash Gun do not work may be rust at contact point like hotshoe or Cells .So it Should be remove by abrasive paper.
If does not work too. It may be some parts out of order like Electric capacity or Transistor.which should be check by meter.
Furthermore old type flash gun may not suit for DSLR since the trigger voltage is too high will damage the camera.
I am sorrry for no idea about flash tubes since rare replace it. |
Der_uli
Tinkerer
Username: Der_uli
Post Number: 14
Registered: 05-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 08, 2010 - 07:27 am: |
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For the pricier versions of flashbulbs you may find technical data at Perkin Elmer's website. The little ones in photgraphic equipment all share similar properties: around 300-400 Volts and several wattseconds of energy. You only have to look for similar length and diameter. Hobby electronics stores carry them, e.g. http://www.conrad.de/ce/de/FastSearch.html?search=blitzroehre&=Schnellsuche&init ial=true here in Germany. |
Mareklew
Tinkerer
Username: Mareklew
Post Number: 177
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 10, 2010 - 08:34 am: |
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There are few factors to xenon discharge tubes (flash tubes). First rule of thumb: if it fits, and is a flash tube, it fits. That's good news.
To elaborate more:
mechanical approach
For a given xenon pressure in the tube:
- the length of the tube is proportional to the *operating* voltage.
- the cross section of the inner cavity is proportional (albeit not in a directly linear fashion) to the current carrying capacity of the tube.
- the glass thickness (proportion between inner and outer diameter) can say things about how far can the tube be overdriven in short pulses, as well as whether it is a flash or a stroboscope tube.
- The shape and material of power electrodes, as well as the form and type of the igniting electrode influence the required voltage and energy of igniting pulse.
As you can see, all these parameters are almost purely mechanical, so you can pick a replacement by calipers and eye. The only thing you don't and won't figure out, is the xenon pressure. Luckily though, as long as you purchase a *flash* xenon tube, it was designed to work in a *flash* gun, i.e. the xenon pressure is optimal for the tube size. You can also assume the same holds true for the original tube...
electric side
Flashguns charge a capacitor (or a pack of capacitors) to some relatively high voltage and then dump the charge into the flash tube. If you open the gun, you will find this capacitor easily - it's going to be the biggest one there.
WATCH IT! It may be charged! Often the flashgun will charge and can't fire, these capacitors can hold dangerous residual voltage even a day after!.
Read its rating.
Say, we have a 850µF/350V part there.
E = U²·C/2
Charged capacitor will hold maximum
E = 350²·850 / 2000000 = 52J
(or 52Ws, if you prefer).
Flash will discharge this capacitor down to about 50-70V, so there's going to be some energy left over, also, the initial voltage will rarely reach the full rating of the power capacitor - this would leave no safety margin whatsoever. It would be safer to assume 10% margin, thus:
Ef = ((350·0.9)²-50²)·850/2000000 = 41J
Your new tube must be able to carry flash energy of 40-50J, have self-ignite voltage above 350V and operating voltage of about 250-300V to fit this example flash gun.
Note also, that some flash tubes have color compensation filter and some don't. If you care for color slides or mixing light, you might need to match this aspect too.
Marek |
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