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How to find something we talked about 1 or 2 years ago???

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gary350

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We talked about industrial SCRs that I have. My SCRs have 2 trigger wires instead of 1. I think the #20 red wire and 120 amp red wire are connected but not sure. I have 6 of these I need to test to see if they are good. We talked about these years ago now I have a project for them. Also need to know if SCRs are npn or pnp devices.

SCR numbers 71RC12 and 9051AR rated 120a and maybe 600v
 
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ChrisP58

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SCRs are three junction, four layer parts, so they're PNPN devices.

They can be roughly modeled as a cross coupled PNP - NPN transistor pair.
 

Reloadron

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We talked about industrial SCRs that I have. My SCRs have 2 trigger wires instead of 1. I think the #20 red wire and 120 amp red wire are connected but not sure. I have 6 of these I need to test to see if they are good. We talked about these years ago now I have a project for them. Also need to know if SCRs are npn or pnp devices.

SCR numbers 71RC12 and 9051AR rated 120a and maybe 600v
You are describing what sounds like a stud mount SCR where the stud is the Anode and the heavy red wire is the Cathode. The two light gauge wires are the Gate which is generally White and the Auxiliary Cathode which is Red and connected to the heavy red Cathode, they are the same. Give this a read and page 2 of 4 shows a few basic and simple methods to test an SCR on the bench. They can also be tested using an old style VOM like a Simpson 260 or similar analog meter. Note the test mentioned is just a simple bench test and will not show all of the characteristics but in most cases makes for a good simple Go/NoGo test.

Ron
 
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