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Transistor Question

Discussion in 'General Electronics Discussion' started by quantumtangles, Jan 11, 2014.

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  1. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Populating the board of a cool AM radio kit today ebayed from a University in Thailand. Pleased with it but one of the transistors looked damaged and when I handled it to move the pins apart, the emitter almost fell off, but it is plainly and terminally defunct (metal fatigue loss of tensile strength just before a pin comes away in your hand).

    It is one of three CS9013 (NPN) transistors working alongside two CS9012 (PNP) transistors and further up the board there are three 2SC3194 NPNs.

    I ask myself whether I can plant any general purpose NPN in its place, or whether I should replace all three of the CS9013 NPNs. Then I think maybe I should also replace the CS9012 PNPs as well because they must be working in tandem with the CS9013 NPNs.

    Its a nice little kit, had for the price of a couple of coffees at Starbucks and I would love to fire it up with a 6v battery (or maybe a 9v battery and a voltage regulator.

    Should I go berserk and replace all the paired 9012/9013 transistors or can I get away with planting a general purpose NPN transistor in the spot where the defunct CS9013 would have gone?

    Or should I stop asking stupid questions and just experiment with general purpose transistors from my parts bin :D

    Thanks in advance for any responses

    Edit: Sorry there is only one CS9012 and three CS9013s
     

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    Last edited: Jan 11, 2014
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,832
    Jan 21, 2010
    The obvious thing to do is to get in contact with the seller and tell them that one transistor seemed to have a defect in a lead and ask them to send you another one.

    If you're feeling particularly good-willed you might offer to do something by way of payment for postage.

    You don't show the schematic (haha -- I see it now).

    OK, it probably wouldn't hurt a great deal to just replace it with some similar general purpose NPN transistor. If you're keen, replace the other with its complement. I doubt that these transistors are matched pairs (or you would have paid more than the price of a cup of coffee).

    There's a maximum of one pair that is affected. If the circuit uses other NPN and PNP transistors, they are not affected (only the output uses a complementary pair). If another of these transistor is used elsewhere, you can take it out and use that, then replace it with some other similar transistor (and a better reading of your message indicates that this is indeed the case)

    I'll try to find you an equivalent for the broken 2SC9013. Here is the datasheet. Take a good one and use it for the output, then grab a 2N2222 or a BC548, or pretty much any other small signal NPN transistor as a replacement. Be careful that you know which leads are base, emitter, an collector on the replacement, they may be different from the original.

    It does look like a cool kit for a beginner. Do you have a link to this kit in ebay or elsewhere?

    And lastly, it's generally best to make sure you don't bend the leads too close to the case. I'm prepared to accept this wasn't the issue here, but as a general rule, it's best to leave a slight gap before you start the bend.
     
  3. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Thanks Steve. The Ebay link I used was http://www.ebay.com/itm/AM-Tuner-Ra...pt=US_Ham_Radio_Receivers&hash=item1e8547c7ae

    The name of the vendor on Ebay is Jeepbangkok and the item was item number
    141150677472.

    I will scan and post the vendor's schematic and instructions. There is a large list of further kits on the flip side of the instructions that looks intriguing.

    I was drawn to the kit because it is relatively unusual to see AM radio kits with more than one (or indeed any) RF inductors, and the PCB is relatively good quality. The RF inductors (in case some readers do not know what they are, are the little metal boxes with coloured screws on top that you can adjust to change the frequency response) should be fun to play around with. Aside from Germanium diode (crystal) radios made on breadboards, of which I have probably made disassembled and remade hundreds of times, this is my third AM radio kit. I figure you probably need to have made ten or more radio kits before you can pretend to know what you are doing. I confess I prefer FM kits because the sound quality is better with FM receivers.

    Going to look at the datasheet carefully and follow the transistor advice to see if I can learn something about these wonderful devices :D
     
    Last edited: Jan 11, 2014
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Steve, I don't think the CS9013 is a 2SC9013. According to the docs, the CS9012 is a PNP, and 2SC devices can't be PNP, so CS isn't an alias for 2SC. Also, I get a lot of hits for CS9012 and CS9013.
     
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