Minimum hfe

If time is valuable then why do the work in the least efficient way?

make a meter.

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umop apisdn 


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I guess I made some assumptions. Is this to be push-pull amp ?

In what way do you think this amp labour inefficient? If I can get it to work without a meter & binning, why build a meter, test & bin?

The amp itself will effectively test hfe, crudely but I think adquately. If the speaker doesnt give a good thunk when power's applied, the trs don't have enough gain. And I wouldn't expect that to happen often.

The main thing I haven't done yet is work out the acceptable value ranges for all the components. It would be an advantage to not have to stick to the single values currently used.

NT

Is he Chinese?

Your so correct there, sorry, I meant to use Xc :)

Jamie

Theoretically, with random NPN Si scrap transistors(*) small-signal input driver and power output, the current gain could range from about

100 to 5,000. But...but...billy goat but... Random scrap transistors can be PNP, NPN, jFETs, DMOSfets, MOSfets, and perhaps SCRs, triacs, diacs, etc. Therefore, you MUST bin them!

I'm fascinated more by the project than the specific parts. Can you expand on the system? Is this two-transistor circuit the WHOLE thing? Or just part of a larger thing? What does the whole thing do. Driving a speaker with what? Why? I asked how many would be built. "lots" is not a number that anybody can deal with. And are they all built at the same place? OR 3 at a time by people who never talked to one another? What are the logistics of the supply chain? Lots of leftover good stuff from a warehouse? Or random radio scavenged from a bombed-out HumVee.

And there's the whole reliability issue. How long does the speaker last when the free transistor goes up in smoke? Being frugal takes a lot more thought than just doing it right.

As for test equipment...Harbor Freight has a multimeter free, no purchase required. Plug your transistor in the socket and the mystery is over. Coupon shows up in the newspaper several times a year. Pile all your friends in the minivan and raid HF. You'll have as many meters as you have friends. I think I have six of them...and I don't have a minivan or any friends.

I routinely buy whole reels of transistors for a buck at swapmeets. And I'm sure the seller isn't losing any money. The world if full of parts past their expiration date. No reputable SMT assembly house will touch them. They're going somewhere. Find out where and intercept them. They might be happier with a $200 charitable donation than the 50-cents a pound they get from the scrap dealer.

5,000 at a pop might put a dent in your requirements for far less money than has been wasted by the participants of this thread. Time is money.

o

o work without a meter& binning, why build a meter, test& bin?

. If the speaker doesnt give a good thunk when power's applied, the trs don 't have enough gain. And I wouldn't expect that to happen often.

es for all the components. It would be an advantage to not have to stick to the single values currently used.

They sometimes will be. They will be tested just enough to determine pinout and whether theyre npn. If they are they go into the product with no furth er testing. The product itself does the last testing stage: the speaker nee ds to give a good clunk when powered up, otherwise there's not enough combi ned gain. The majority of unidentified small trannies are usable npn, the r est are mostly pnp. The plan is that this is all the testing required to en sure 95% succses.

NT

The idea is for people in poverty to build active computer speakers and sel l them, using nothing but scrap. The circuit is all the electronics that's involved, there's also a speaker or 2, a couple of leads and a speaker cabi net or 2.

Lots of people in various countries can each build small quantities. There are many countries in the 3rd world where the necessary scrap is available.

See dumped garbage, poke it, and if you spot some electronics you can proba bly build something.

Depends on Vcc, speaker R & speaker power rating. How long something lasts when already dead isn't a high priority though.

Nothing like that exists in the 3rd world.

$1 is unaffordable, never mind $200. This project is aimed at people making under $1.25 a day. In the community I'm most familiar with people live on about 30c a day, and mouldy bread is an important part of the diet. Solderi ng will be done using a nail or other bit of scrap metal heated in the cook ing fire. Solder will be recovered from boards, flux made from scraps and s o on.

Once this is all done the plan is to distribute the plans internationally v ia Penny Library.

I appreciate all the input on this. Naturally its not something I can work full time on, but I look forward to seeing this working out there in the wo rld where its very much needed.

NT

a scrap lousdpeaker typically comes in a cabinet attached to an amplifier so just patch a headphone cable into the wiper on the volume knob and call it done.

how big's the market for these things?

also assuming they can recover solder without poisoning their kids, what are they using for flux?

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umop apisdn 


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Either I misunderstand you or you're suggesting there's working equipment on 3rd world dumps.

Everyone that has a computer, wants sound at the cheapest possible price, and is willing to buy from a street vendor.

I've yet to do flux tests, I expect the most likely contenders are going to be wood resin, soap, oil and dripping.

NT

Then perhaps you should switch to a functional operating system?

Best regards, Piotr