false economy?

Discussion in 'General Electronics Chat' started by Roob, Mar 21, 2015.

  1. Roob

    Thread Starter Member

    Mar 21, 2015
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    I just bought 100 2n3904 unbranded transistors from eBay free postage from China.

    For 99p

    ?

    These are 34p from Farnell plus £5 postage

    Will they work?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If this is for your guitar fuzz pedal, then probably not. I recall the 3904 and 3906 to be silicon transistors, not germanium
     
  3. Roob

    Thread Starter Member

    Mar 21, 2015
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    They are for that but the circuit also specifies these in addition to the germanium ones. 2 of these and 2 germanium I think.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    If they work then good enough. I've bought their mates (PN2222A) for $6/1000. They weren't labeled either. Since these are general purpose transistors you probably shouldn't expect too much from them. 300mw dissipation, around 50 for the beta, 300Mhz roll off (if you're lucky).
     
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  5. Roob

    Thread Starter Member

    Mar 21, 2015
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    They are for audio signals. I guess 20khz is ok.

    Question is would the Branded be better?

    I'm new so forgive- do we want large or small power dissipation, large or small beta?
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    To answer your question, yes, 99% of the time the Chinese made up branded items are fine.

    Look at Farnell's price for 1000 pieces. You will see that a few cents or even less than a cent on some items as you get high quantities. Often times, the sellers from China are selling the extras from a production run, or items made on the weekend 'under the radar' with equipment from a branded manufacturer, or from a "box that 'fell' off of a truck".

    In any case, international postage out of China is much cheaper than it would be to ship from the US back to China. So, in the end, you are likely helping some poor family or (some crime syndicate family) earn some fraction of a dollar per package. Either way, Farnell or Digikey would likely prefer to have $0.99 purchased routed somewhere else, even if they so sell each transistor for $0.50 when you buy less than 10, it doesn't pay for the cardboard box, tape, shipping label, conveyor belt power and labor to pick the item from the warehouse and package it.
     
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  7. Wendy

    Moderator

    Mar 24, 2008
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    Branded are more consistent. Thing is, transistors can be funny. On some oscillator circuits and a few audio it matters a lot, but most cases not so much. Proper design tends to remove the variations. Transistors in specific are known to very hugely in a family, though they tend to be the same for a lot (from the same wafer).
     
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  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    On a production line there will be a variability of product quality.

    With mass produced small items it can be cheaper to ditch (sell off cheaply) an entire batch if the batch average is not up to standard, than to sort out the good from the bad.

    What Bill is telling you is that an amateur can afford the time to make this sort, so if you are prepared to do this and also perhaps not use the products in mission critical situations, this can be a way of effectively and cheaply getting a lot of good transistors. But don't expect them all to be good.

    Incidentally many of the DIY retail chains give 'exclusive special offers' on all sorts of things from power tools to screws.
    These often have a slightly different model number you won't see elsewhere.
    These are also often production line fallouts.
    That said they again may be good for occasional(amateur) use.
    The words 'not for commercial use' is a clue.
     
  9. Roob

    Thread Starter Member

    Mar 21, 2015
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    My small scale can handle a bit if extra testing and trialing so the only question is:

    Is a functioning cheap "snide" transistor going to be as good as a Farnell, digikey one?
     
  10. MCU88

    Member

    Mar 12, 2015
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    Mate just go with an 2N3904 NPN transistor at Tayda Electronics for USD 2-cents and be done with it.
     
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  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It depends. If you don't like how your fuzz box sounds, then it could be the 2N3904 transistors. However, there is so much variation in the germanium transistors and the fuzz face / fuzz box circuit is so sensitive to the gain of the germanium transistors that box each one has its own unique sound unless all parameters of the germanium transistors are matched to those in another box. Therefore I would say, the likelihood that you can identify variations between various silicon transistors is doubtful. Those transistors are not pushed to their fuzz-making limit like the germaniums and silicon transistors are inherently more reliable and consistent than germanium in the first place.

    As suggested above, why order no-name transistors for 1 cent apiece on eBay when you can order brand-name transistors from Taydaelectronics.com for 2 cents each.
     
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