Transistor Question

Isn't the BC108C an NPN, and the 2N series PNP?

no, the 2N series is both NPN and PNP.

What I suggest is getting the datasheet for your BC108C, then look through the data sheets for 2N parts and find one similar. Or just buy the BC108C from Newark.

I wish I could order from another supplier, but I'm afraid my hands are all tied up with red tape. Even worse, the supplier (an educational outfit) I'm ordering from does not list the manufacturer of their transistors or supply a data sheet!

You can google up a datasheet, and go to any online distributor's catalog to compare specs, then choose your part. It's really simple.

NTE Electronics tells me that the BC108C is the same as their NTE123A, which is a pretty generic transistor. Any 2Nxxx that crosses to the NTE123A should also meet these specifications. But check the data sheets.

Can you give us a clue as to what its being used as / for?

An equivalent transistor may have slightly different specs which could be important to the way you are using the BC108C

The BC108C is a general purpose, low power, medium frequency, NPN transistor.

The 'C' at the end denotes that its been selected for current gain, so the same transistor can be bought as an 'A', 'B', 'C' version.

This may not matter if your circuit is just using it as a switch, but it may do.

type it into this web site to get a full data sheet of any (almost) transistor.

www.alldatasheet.com

John.

The transistor is for a small amplifier. I'm having my class put together an amplifier circuit as a class project, hence having to order from an educational supplier that does not list any specifics about their devices and my limited knowledge of devices.

The notes on the circuit say that any high gain transistor could be used, perhaps one of you could suggest a good transistor for that purpose.

Are the specifics on transistors really that important for non-critical applications such as mine?

The specs don't matter that much if it's just any old amplifier (presumably DC or audio??). As long as it's got about the right gain, and will take the voltage, it should be fine.

Only problem could be with wiring (making sure the (b,c,e) end up in the right place) - are you using a ready-laid-out PCB, doing one yourselves, or using breadboard/strip-board etc.?

[Edit - can you give us a link to your supplier, so we could check out what they stock?]

Due to the environment that my students are in, we're just using bread boards. The amplifier is a very simple two transistor audio amplifier. I finally cross referenced a cross reference (through one of the data sheet websites) and found a 2N transistor with suitable gain that matched one they had listed. Here's a link to their transistor selection.

http://www.kelvin.com/Merchant2/merchant.mv?Screen=CTGY&Store_Code=K&Category_Code=ELPCTO

Go to Mouser Electronics and type in BC108C.

You will find that this part cross-references to NTE123A. Link

NTE123A is an NPN general purpose complementary transitor in a TO18 type case. This transistor is designed for applications such as medium-speed switching and amplifiers from audio to VHF frequencies.

Features are

Low collector saturation voltage: 1V (max)

High current gain-bandwidth Product: ft=300Mhz(min) @ Ic20mA

The data sheet can be downloaded and printed. I recommend that you do this as I did. All of the electrical characteristics are given on the data sheet.

I was unable to paste the pdf file of the datasheet here, but you can get it.

Convert your PDF to a JPG, and then CR4 will accept it.

Good stuff, Thanks eriew! I use mouser a lot for some of my personal projects.

2N2222 is really common general purpose NPN ...should do the job you could google it to check it's ratings.

You must be a lazybone who dont type any more words on the google or yahoo or cine etc for your results.

if you post your circuit scheme, we can propose a similar one for you. its not too difficult to do.

I seem to hear this device somewhere. as indicated above threads.

you may change it with 9013, 8050 or said as D.CAT

or buy anone may do the trick.

Ooooo DAG I don't mean to be critical but that circuit is lousy!!!

The transistor biasing is dependent on the transistor gain... Yuck!

The headphones supply dc to the final stage and so will be distorted...

5 volts is not enough to keep the transistors out of saturation / clipping and I don't think I saw one dc decoupling capacitor!!!

In fact I would go so far as to say its worse than lousy its a terrible circuit!!!

Otherwise it might work!!

John

Well, I know just enough to be dangerous! Can you recommend a better circuit or appropriate modifications?

My main goal is illustration of concepts and some interest clenching hands-on activity. The amp will drive some student built speakers.

I will sketch one up for you if you tell me what the input voltage source is roughly, so I can calculate the gain required etc...

John.

I was planning to power it with my lab power supply. 5 volts at 3 amps or variable 0-3 volts at 1 amp.

I'm now reading up on biasing to better understand the shortfalls of the circuit...

Hi,DAG,

you cannt get 3A at speaker from 5V . most of speaker has 4ohm at the least. so you can only get 1App.

if you give student an activity content. I suggest you show them a simp;le circuit, which I post at " a simple circuit"

http://cr4.globalspec.com/thread/23137#comment264012

LG DAVE and Sparkstation give a wonderful example.

I thik students will delight at it.

Sorry , I may mistake your meaning.

if you will show your student and will cause thheir interest. I suggest you use a IC, say LM358 for this goal.

its very easy, neednt modify

Here's one that's a little better: http://english.cxem.net/amplifier/amplifier66.php

I found it here: http://www.discovercircuits.com/list.htm#A

This place has over 7000 schematics, and not just amplifiers. It'sa very handy resource.

Very nice! I love the site. Thanks!

yes google first ask questions later, or was that shoot?

anyway a BC547C is a substitute

http://www.google.co.jp/search?hl=ja&lr=&q=bc108+substitutes+transistor&start=10&sa=N

And PN100 (NPN) and PN200 (PNP) are common generic types that will replace most garden variety transistors. Especially if it's just a simple amplifier or switching application.