transistor pinout help

[daz]

i'm trying to find the pinout for this transistor but i was getting conflicting info. So on the NTE site i looked for it but those NTE pinouts drawings always confuse me as to which side i'm looking at, the round side or the flat side. Heres the pdf....
http://www.nteinc.com/specs/100to199/pdf/nte123ap.pdf
is that the flat or round side i'm looking at?

[JoeM]

Flat side.

I think that cross references to this:

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

[g1]

You can run into trouble with NTE pinouts. Often they offer a number as a replacement with the stipulation that the pinout may be different from the original transistor.
If the transistor you are looking for the pinout for is not an NTE123AP, please post the number of the original.
As far as your question, you are seeing the flat (front) side. The drawing below shows the pins in the same order, with the transistor flat on it's back, looking at the pins.

[Jazz P Bass]

That drawing is clearly the flat side.
That is what the two lines on either side indicate.
The taper of the flat into the ends.
If you were looking at the round side, would there be lines?
No.
(Dotted ones, perhaps)

[daz]

I crossed it to 123ap but it's got the generic number 2N3904. Beside the pinout which I think i have (see image below), I also need to be sure if this will work in place of a BC238 or BC239, both of which cross to a 123ap as does the 2N3904. But being twice removed i start wondering if things are getting lost in the translation if you know what i mean.

Google Image Result for http://www.elektropage.com/images/upload/2N3904_E98ZD.gif

[JoeM]

What application is this for?

[Steve Conner]

American "2N" series transistors in TO92 packages, with the flat printed face towards you and the leads sticking out the bottom, from left to right the leads are "EBC".

The BC238 and 239, like every other TO92 BC series transistor I tried, are "CBE". If you swap a 2N for a BC you have to turn it 180 degrees.

A well-designed transistor circuit won't be too fussy about the exact type of transistor, as long as you hook it up the right way round. The 2N3904 is a commonly available general purpose NPN transistor and I use lots of them.

[Jazz P Bass]

The 2N3904 is so common, Radio Shack carries them.

[Enzo]

Daz, try this approach. You need to know about a transistor, it says 2N3904 on it. Look that up at Mouser. They have 10 different ones of that type, pick one and open the data sheet link. Here is one:

http://www.mouser.com/ds/2/149/2N3904-82270.pdf

I think the pinout drawing is pretty clear. AH, that seems to be the same sheet Joe linked us to, sorry. So whenever possible, look for the real deal, not for something that is supposed to be just similar.

Note the cost is as low as about 15 cents. I see the NTE part going for more like $1.15, and while it covers that 2N3904, its specs are a lot closer to a 2N4401, and that sells for about a dime each. So if you can get useful information from the NTE guide, by all means do so, I keep their book on my shelf too. But never BUY the stuff.


The NTE guide tells you which of THEIR transistors might work in place of yours. What it does not say is that all things their parts cross to are interchangeable. For example 2N3904 is a 40v 200ma NPN transistor, crosses to the NTE123AP. MY 2N4401 also crosses to the NTE123AP, but it is a 40v 600ma NPN transistor. MY 2N4401 would work OK in place of your 2N3904, but your 2N3904 could fall way short trying to drive a relay or lamp or something that used more that 200ma while my 2N4401 would be happy. SO never use the cross reference in place of real specs. It IS useful to see what a completely unknown part might cross to, but the reverse cannot be trusted.

You want to use it in place of a BC238? Look up BC238 then, either google, or just Mouser. I find the BC238 is a 25v 100ma part. Your 2N3904 would probably work in its place - following Steve's advice on turning it around - but the BC238 would very likely fall short trying to sub the other way.

[daz]

Thanks all. The 3904 only because it's what i had. I'm going to throw together a treble booster with it, and i'm not sure how important what i use is but i will probably socket it so if i need to i can swap easily.

[Steve Conner]

The old germanium transistors really make a difference to a treble boost circuit. Some of them had such lousy frequency response that the "treble" boost would run out of steam somewhere in the upper midrange. A modern silicon device will keep on amplifying right through the audio band, up into the 10s of MHz.

[km6xz]

Daz, the transistor substitution books can potentially get you into trouble like Enzo said. The best way to find a substitution is look up the main specs of the transistor you are replacing and and look for other transistors with at least the max current and key voltages, and for sake of reducing confusion, the same pinout. That is really easy do nowadays with the internet that allows searching for any data sheet imaginable. Dealers like Mouser let you enter parameters you get from the data sheet and find all the transistors with have those specs. There might be many.
http://ru.mouser.com/Semiconductors/...BJT/_/N-ax1sh/

I would not trust the NTE book, they are trying to fit every transistor into a limited number of products they offer. Sometimes the NTE part is actually the part you are looking for, but with the NTE number on it. A really common transistor like the 2n3904 or 2n2222a probably crosses to those exact parts simply because they are so common that they can get them for very low prices. For example the 2n3904 in 2,000 lot prices are only $0.03 each and NTE marks them up to over $1.00 which is a pretty nice profit.
The biggest problem with NTE or before that, ECG or HEP is you never know what you really are getting. Most of the time it works fine not to have the original specs but sometimes it is really important and only knowing the circuit really well can tell you which case is which. Putting in a transistor that just does not meet the circuit needs can he hard to trouble shoot.

[J M Fahey]

Thanks all. The 3904 only because it's what i had. I'm going to throw together a treble booster with it, and i'm not sure how important what i use is but i will probably socket it so if i need to i can swap easily.

Well, in that particular case most *any* transistor will do, we are talking a 9V battery powered circuit, passing only 1 or 2 mA.

Get *any* 10 cents NPN general purpose transistor (forget NTE) and check pinout for proper wiring, nothing else.