Discussion in 'Lighting Equipment' started by royall_berndt, Jan 5, 2021.
I used to see plans in.magazines for constructing flash triggers. Anyone have those plans?
I have no idea what type of trigger in that magazine but I have seen other optical trigger using Light Activated SCR.
The magazine trigger used an LA SCR.
Good luck finding one of those these days.
I built an opto-slave years ago using a photodiode, a transistor and a low gate current SCR. Plus a couple of resistors, a zener diode and a capacitor to power the thing from the flash trigger voltage.
These days it would cost more in components, connectors and a transparent housing than you could buy one for.
Sunpak and other makers sold little 'peanut' slave triggers with a rubber sucker for mounting. They're quite plentiful and crop up for sale quite regularly and cheaply.
Afraid Joe hit the nail on the head. I had the same idea years back and couldn't find a LASCAR or LA SCR anyplace.
As far as I know, this is the favorite use for LASCRs.
I came across my old homemade slave trigger the other day. So for the sake of completeness; here's a picture of it and its CCT diagram.
And the circuit -
The MRD14B is a photo-darlington transistor. Good luck finding one of those these days! As well as sourcing a C-106 sensitive gate SCR... or a small transparent plastic box... or a male line P-C plug.
I suppose a photo-darlington could be fabricated by cutting the top off a metal TO-18 cased device and filling it with transparent epoxy resin. But really, is it worth the cost and trouble?
Unless constructing junk-bin electronics is your idea of fun.
Oh, nearly forgot. The circuit was designed to be 'self-powered' using the small current available from an old high trigger voltage flash. Hence the 1.5 megohm resistor. With a modern low trigger voltage flash that resistor could be replaced with a much lower value, or even with a short. And any consequences from using the above design are entirely at your own risk. I take no responsibility!
I think you can now get photo-SCRs, so maybe no need for photo-darlington
My first real electronics project, real enough to get in a box, is (I still have it somewhere) a touch switch from Popular Science.
It uses the C106B1, which looks like the one you have. I built that in about 4th grade, after mail ordering the SCR and the NE-83 from Allied Electronics.
Otherwise, you get the reverse PC from a PC extension.
I still have the PC cord for my Vivitar 283. One could cut off the PC end, and splice directly onto the rest of the cable.
Or splice directly onto a hot-shoe to PC adapter.
It seems that the MRD14B is so old, it is in a museum!
MRD 14B, Tube MRD14B; Röhre MRD 14B ID67140, Transistor
Three photo-darlington from Digi-Key:
Sensors, Transducers | Optical Sensors - Phototransistors | DigiKey
The touch switch is in this one:
I used a regular box, though, and then built a new box for it in
metal shop in 7th grade.
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