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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Jul 2020, 11:53 am   #21
60 oldjohn
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Default Re: Which transistor

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Originally Posted by G6Tanuki View Post
There was a bunch of 'reversible' PNP transistors produced back in the 60s and often used as things like relay/solenoid-drivers in first-generation electronic telephone exchanges: these invariably had low-gain [Hfe of 30?] .
I have just measured a doubled up BC547s on my Peak tester. Single transistor Hfe 500, two together, NPN Silicon Transistor Hfe 19. I may try them in a circuit.

John.
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Old 2nd Jul 2020, 2:01 pm   #22
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Default Re: Which transistor

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When using breadboard I have back to back diodes save getting them wrong.
I remember setting something up for an expensive test saying "It's not working", groans all round. Then I said "Oops current limit too low", cheers all round. The test went well.
 
Old 2nd Jul 2020, 3:33 pm   #23
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Default Re: Which transistor

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I have just measured a doubled up BC547s on my Peak tester. Single transistor Hfe 500, two together, NPN Silicon Transistor Hfe 19.
What does one backwards give as an Hfe?
 
Old 2nd Jul 2020, 4:53 pm   #24
60 oldjohn
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Default Re: Which transistor

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Originally Posted by merlinmaxwell View Post
Quote:
I have just measured a doubled up BC547s on my Peak tester. Single transistor Hfe 500, two together, NPN Silicon Transistor Hfe 19.
What does one backwards give as an Hfe?
I will have to get a different tester out tomorrow. The Peak sorts it out automatically, so can not get it reversed.

John.
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Old 3rd Jul 2020, 10:30 pm   #25
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Default Re: Which transistor

In reverse one transistor measures nearly 10Hfe two transistors connected c-e b-b e-c = 19 so the Hfe are added together.

John.
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