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I found a one pulse activated automatic trigger circuit and it has A509 and C509 Transistors to be used. But, these transistors are extremely rare and very hard to find. eBay has those both, but it is not worth to buy according to huge import charges and shipping fees.

Circuit Diagram: enter image description here

Please can you recommend best equivalent transistors for A509 PNP and C509 NPN Transistors?

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    \$\begingroup\$ just about any jelly bean PNP, NPN combo should do in this circuit. \$\endgroup\$ – JIm Dearden Jan 28 '17 at 16:11
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Pretty much any el cheapo transistor will do. Don't pick the fancy types.

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  • \$\begingroup\$ Thanks very much......As I am paranoid in choosing equivalents, please I need two best equal complementary transistors NPN and PNP suggestion from you. Can I use BC635 NPN and BC636 PNP Transistors here? \$\endgroup\$ – StartX596 Jan 28 '17 at 16:16
  • \$\begingroup\$ the transistors take 300ma of current (higher if the bulb is cold) and dissipate maybe 500mw. so any run-off the mill small signal transistor would work, like to92. I would have picked 2n5551/5401 but that's just because I have a gazillion of them. the BC635/636 will work as well. if they work in hot environment, you may try the beefier to126 ones. \$\endgroup\$ – dannyf Jan 28 '17 at 17:30
  • \$\begingroup\$ It is safe to buy two TO-126 ones before assembling, so can you tell what TO-126 Combo you use if you are assembling this circuit? \$\endgroup\$ – StartX596 Jan 29 '17 at 1:23
  • \$\begingroup\$ Will D1225 NPN and B909 PNP work here? \$\endgroup\$ – StartX596 Jan 29 '17 at 13:00
  • \$\begingroup\$ > Will D1225 NPN and B909 PNP work here? sure. I would have used bd13x/14x but that's just because I have lots of them. \$\endgroup\$ – dannyf Feb 1 '17 at 21:37

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