Transistor Question - Page 1
Forum section: electronics / beginners

author: Fisher77
author_rank: Regular Contributor
timestamp: December 18, 2016, 12:29:28 am
content: Will a 2n3906 work in place of a BC328? I have the 2n3906's on hand. I looked at the datasheets for both. I did not see much of a difference, but thought I would ask to make sure. I also found that the BC328 had been replaced by the BC327, and that both are now obsolete. If there is a better match than the 2n3906 please let me know.Thanks

author: xrunner
author_rank: Super Contributor
timestamp: December 18, 2016, 12:42:35 am
content: Hard to answer without a little more info as to the type of circuit the transistor is operating in - basic switching maybe OK ... But, if you want to drop it in as a replacement be aware that the pins of these two transistors are not the same (emitter and collector are reversed) when looking at the "front" of the package.

author: Audioguru
author_rank: Super Contributor
timestamp: December 18, 2016, 01:29:14 am
content: Didn't you notice that the maximum current for a BC327 or BC328 is 800mA but for a 2N3906 it is one-quarter at only 200mA?I would use a 2N4403 that has a max current rating of 600mA.

author: Fisher77
author_rank: Regular Contributor
timestamp: December 18, 2016, 03:37:16 am
content: Quote from: xrunner on December 18, 2016, 12:42:35 amThe circuit is the Blue Ring TesterQuote from: Audioguru on December 18, 2016, 01:29:14 amI missed that. Thanks for pointing that out Audioguru.

author: onlooker
author_rank: Frequent Contributor
timestamp: December 18, 2016, 04:20:52 am
content: The 270R resistor on Q1's collector should limit the EC current ~<20mA and Q1 is fed by a ~10Hzsaw tooth2.5ms wide inverted pulse signal (generated by IC1a). It looks like any generic small signal transistor can be used for Q1.Edited: Also the the collector of Q1 outputs a ~10Hz 2.5ms wide pulse signal.

author: hamster_nz
author_rank: Super Contributor
timestamp: December 18, 2016, 04:25:02 am
content: It looks to have at most 20mA of current through it (6V across a R8 and D2), and looks to be acting a a switch... can't see any reason why any other 'jellybean' transistor couldn't replace it.But I am no expert...edit: corrected math due to D2.

author: Fisher77
author_rank: Regular Contributor
timestamp: December 18, 2016, 06:20:00 am
content: I appreciate the help

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 18, 2016, 06:51:38 am
content: Yep pretty much any PNP general purpose transistor will work. Get one with the pinout that works for you.Just discovered what the "Blue Ring" tester does, viz , counts the ring down cycles of an inductor.Here's another variant of the same circuit, they use 2N3904 as a NPN follower (on that basis you should be able to use a PNP 2N3906 in the inverter configuration of your circuit).https://www.flippers.com/pdfs/BLUE_rt_assembly_manual.pdfmore info/historyhttp://members.ozemail.com.au/~bobpar/fbt.htm

author: Fisher77
author_rank: Regular Contributor
timestamp: December 18, 2016, 08:30:56 am
content: Thanks salbayeng. I may go with that anatek version.Here is the one I was looking at:http://www.flippers.com/pdfs/k7205.pdf

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 19, 2016, 11:46:37 am
content: Ah It's a good old Dick Smith kit (an Australian version of Heathkit?).Back then we were using mostly European transistors, hence the BC part number.The "basic general purpose transistor" was a BC108 in a metal can (=BC548 in plastic) , the BC107 (BC547) is the same but selected for higher voltage, and the BC109 (BC549) is the same but selected for lower noise.And BC557,558,559 the same in PNP.The above were also binned by hFE , so BC108A was~100 , BC108B ~ 200 , BC108C ~300 etcAlmost all european transistors have base in the middle.The above are similar to the 2n3903/4/5/6 (these American transistors have base in the middle but are mirror image!!!)BC327, BC328 are higher current versions of the above (800mA vs 300mA?) So maybe like a 2N2222?Many American transistors have the collector in the middle. That's because the "substrate" is normally soldered onto a little paddle in the lead frame on the centre pin. And the "substrate" is the collector for junction transistors. For IC's the substrate is the most negative terminal , that's why a LM7805 has gnd in the middle while a LM7905 has the input in the middle.More than 60 years ago, the first transistors were made from thin slabs of germanium, which was the "base" , i.e. the base from which you built the transistor up from, you then then doped a collector on one side and an emitter on the other, so really ancient transistors had the base in the middle. The original transistor symbol was just a vertical bar with a line on either side (the emitter with an arrow).

author: Fisher77
author_rank: Regular Contributor
timestamp: December 20, 2016, 03:07:25 am
content: Thats some good info salbayeng. Whatever happened with the Dick Smith stores? I saw they were closing down, and then I saw they might be bought out and saved by somebody. Here the similar type store to Dick Smith's was Radio Shack. Radio Shack used to be a great place for components, kits, electronics tools, etc. When I was a kid I would spend hours in there looking at all the neat stuff. Fast forward to today when you go in there about all you can get is a damn cell phone.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 21, 2016, 02:37:26 am
content: Back in the early 70's there was nowhere in Australia to buy components and stuff except for some TV repair places, and electrical distributors, but no stock to browse. I bought a lot of stuff from the UK via mail order.Dick Smith was a ham, and saw a need for components/radio supplierrs so started Dick Smith Electronics in mid 1970's? They would make kit designs in conjunction with Electronics Australia magazine.Later on Jaycar started selling retail , and also Altronics , both of these also sell to professionals, and both are a bit like Radio Shack. We also had Tandy over here that were basically RadioShack franchises, it was good in the late 80's, but has faded back now to toys and phones. Altronics and Jaycar are still going strong.Tandy and Dick Smith peaked around 2000 due to the massive boom in PC's and peripheral, however neither was anything like ComputerCity, and pimply faced kids don't sell computers real well!Dick Smith sold out to Woolworths (a supermarket chain) in 2000? more recently some capital investment group bought it out, pumped it up and floated it on the ASX and scampered off with a huge profit. Then due to a whole pile of dodgy accounting practices and mismanagement DSE fell flat on its face just before Christmas last year, and wasn't honouring gift vouchers bought even days before! The stock was sold at a fire sale, and I think it is pretty much gone forever. DSE's undoing was attributed to buying stock with the highest supplier voucher value, rather than buying stock they could actually sell. E.g. they would buy $100k of stock from a particular supplier because these "garden gnomes" came with $40k of vouchers. so on the books your cash is down $100k less the $40k vouchers = -$60k, while inventory is up $100k, so overall your financial report shows a profit of $40k, but in reality you have accumulated a warehouse full of stock this is going obsolete fairly quickly.

author: Audioguru
author_rank: Super Contributor
timestamp: December 21, 2016, 03:46:54 am
content: Radio Shack has been gone from Canada for many years. The last of them sold cell phones then some were bought by Circuit City but they quickly sold out to Bell Canada and now they are called The Source.Owned by Bell Canada then of course they sell cell phones.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 22, 2016, 03:22:39 am
content: Well at least you have Canadian Tire, really need that sort of supplier over here!