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Transistor Orientation woes ?

I'm a novice.

I'm trying to test NTE108 transistor. I found a little circuit that is suppose to test transistors. See diagram below or link.

formatting link
The description of its use is as follows... Testing in a simple switching circuit Connect the transistor into the circuit shown on the right which uses the transistor as a switch. The supply voltage is not critical, anything between 5 and 12V is suitable. This circuit can be quickly built on breadboard for example. Take care to include the 10k resistor in the base connection or you will destroy the transistor as you test it! If the transistor is OK the LED should light when the switch is pressed and not light when the switch is released.

To test a PNP transistor use the same circuit but reverse the LED and the supply voltage.

--------------------

The problem is that when I try to test my 108 it seems to work in the reverse. That is when Emitter is on C and Collector is on E the touching of the 10k Resistor to the 9volts turns the led on. If I connect it up the way the diagram shows me the LED just comes on and stays on. If I connect the

10k to the 9v the light gets a little brighter.

Presumably the problem is that I have the orientation wrong. But when I look at the data sheet I could swear I have it right. I'm afraid I find it a little confusing specially with the fact that it appears that there are at least 3 packages that look the same and have different pin outs eg. TO92A, TO92B, TO92C. I sort of wish that the data sheets would give a 3d diagram. The diagram seems to show two double lines || || to indicate the rounded side of the transistor.(I assume) So looking at the transistor that way the orientation is ||EBC|| . (looking straight on rounded side pins down)

Thus I think mine the NTE-108 T-NPN SI RF/IF/VID AMP is as follows holding the transistor by the pins. Legs down in front of me and with the flat part with the writing away from me and the round part toward me E B C. or looking straight down at the transistor and the pins sticking up in the air with the flat part away from me C.B.E.

Can anyone point me in the right direction. Am I wrong in my orientation, and is the circuit for testing transistors wrong. It works in complete reverse for me.

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Reply to
Martin
Loading thread data ...

supply

include

transistor

and

the

of

way

the

look

at

TO92A,

diagram.

rounded

the

holding

part

air

orientation,

Jamie,

Thanks for your points. By the way something strange is happening regarding this post, I see your response but cannot see my question. It has not showed up on the news group.????

Anyway your scaring me now. How the heck are we suppose to know how to orient the transistors if the diagrams they give us on the packages are wrong ?? Regards

Reply to
Martin

most of the time the lay outs are from the bottom in other words, you look at the transistor upside down. seeing that its a NTE, i wouldn't put it pass them to use a different config for that number the their replacements don't always match the physicals of the original also, you must remember that most of their replacements are nothing more than other transistors that electrically replace but not always physically and includes not matching their own case specs at times. you can't trust NTE in many case, their replacements are not always good depending on the application.

Reply to
Jamie

Im at work right now and cant check that. However I will check that when I get home. As I mentioned right now based on the test the LED stays on and gets a little brighter when I touch the base with the 10k to +. I will try touching the base to ground and see if it goes out. If it does what does that mean (if it does not what does it mean). Thanks.

Reply to
Martin

touching

regarding

showed

diode.

James, The link you sent me is basically the same as the those provided by the datasheet. Im afraid I dont understand your description "The top part of the image is the flat surface" Are you saying that looking at the transistor picture that you provided Im looking at the flat part of the transistor with all the writing on it. If that is so then Ive been completely wrong on how to read these pictures. In other words ||EBC||

Reply to
Martin

formatting link
if that will help you at all. the top part of the image is the flat surface.

it is good double check for the base and emitter. there is a simple way to test for the base and emitter if you have variable voltage source , you inject + volts into what you think is the emitter, and then place the + lead of your DMM on what you think is the base. most transistors will break down at a much lower point in the emitter vs the base to the collect. some common values are around 6 volts, the emitter become a zener diode. some times i see that using a DMM in Diode mode you can get a lower forward reading on the BE side but don't depend on that.. you should have a DMM with a transistor checker on it.

Reply to
Jamie

Well that explains a lot. It appears I have been looking at the diagrams incorectly. grrr.

Thanks.

Reply to
Martin 

--
There's the problem!  

The two solid lines on the far left and right of the diagram indicate
the edges of the package while the two inner lines indicate the edges
of the flat. looking at it with the flat _facing_ you.  If the flat
were on the far side, the inner lines would be dashed.  That's an old
drafting convention which is used to show hidden lines.  Another
convention is to visualize a drawing as lying on the bottom of a bowl,
and when the view changes, you slide the old view up the side of the
bowl until it becomes the new view.

So, looking at the NTE108 drawing in that light, the topmost view is
that of a TO-92 package with the flat facing you and the leads
pointing down, the lead order being EBC from left to right.  Then, if
you push that view down it'll slide up the wall of the bowl and you'll
wind up with a bottom view of the package with the lead sequence still
being EBC from left to right.
Reply to
John Fields

supply

include

transistor

and

of

way

look

at

TO92A,

diagram.

the

holding

part

air

Thanks. for the info. Indeed I suppose the little tester I build was telling me the truth. And at least tigged me to the fact that something I was doing was wrong. Frankly while the drafting idea of dashes makes complete sense (NOW), I didnt see anywhere that explained the proper orientation of the || || double lines. Your explanation provides this and it makes sense that you would read it from the flat side that has writing on it.

Thanks.

Reply to
Martin

"Martin" wrote

are

I think it's unlikely that the diagram on the package is wrong. The other poster was just telling you to be wary of NTE cross-refs as the pin-outs don't always match the original part.

What happens if you ground the base when hooked up as the schematic shows (emitter to ground)? The LED should turn off.

Reply to
Anthony Fremont

"Martin" wrote

touching of

the way

the

What if you connect the resistor to ground? The LED should turn off then.

I look

a

are at

TO92A,

diagram.

rounded

way the

You should be looking at the flat side, pins down for the EBC order.

holding

part

the air

No, pins down with flat side towards you (writing visible).

Reply to
Anthony Fremont

Alternately, Radio Shack used to carry (some stores may still have it) an inexpensive "junk box tester" that identifies component leads for BJT and FET transistors, diodes, SCRs, and triacs. Catalog # 22-330.

--
Rich Webb   Norfolk, VA
Reply to
Rich Webb

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