# Identifying the legs of a transistor.

J

#### Joe Norton

Jan 1, 1970
0
Hi,

Very basic question. Could someone remind me which leg is which on a
transistor, starting from the tag on the case.

Thanks,
Joe.

C

#### Chris

Jan 1, 1970
0
Joe said:
Hi,

Very basic question. Could someone remind me which leg is which on a
transistor, starting from the tag on the case.

Thanks,
Joe.

Hi, Joe. Thousands of transistors out there. How about describing it,
and giving any numbers printed on it?

Chris

R

#### Roger Johansson

Jan 1, 1970
0
Joe Norton said:
Very basic question. Could someone remind me which leg is which on a
transistor, starting from the tag on the case.

If there is a tag it is indicating the emitter.

Tagged transistors are very uncommon today, so you will have to rely on
other methods. If we are talking about bipolar transistors they can be
described as two diodes and you can easily find these diodes with the
help of a diode tester (on a modern digital nultimeter).

When you have found the two diodes and how they are joined you know which
pin is the base.

To find out which of the other pins are emitter and collector you can
test both possibilities in the transistor tester. The combination which
gives the highest hFE is very likely to be the right combination.

J

#### Joe Norton

Jan 1, 1970
0
Hi, Joe. Thousands of transistors out there. How about describing it,
and giving any numbers printed on it?

I have two transistors. One is a 2N2219 A and the other is a 2N2905 A.
Both have round metal cases with a tag at the edge. One pin seems to be
connected to the case. Does this help? Please excuse my ignorance!

Joe.

C

#### Chris

Jan 1, 1970
0
Joe said:
I have two transistors. One is a 2N2219 A and the other is a 2N2905 A.
Both have round metal cases with a tag at the edge. One pin seems to be
connected to the case. Does this help? Please excuse my ignorance!

Joe.

Hello again, Joe. If I need a transistor pinout, I'll go to the NTE
Semiconductor cross-reference page first. They sell equivalents for
television/radio repair shops and other service techs.

http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/Search?OpenForm

Your 2N2219 crosses to an NTE123

http://www.nteinc.com/specs/100to199/pdf/nte123.pdf

and your 2N2905 crosses to an NTE128

http://www.nteinc.com/specs/100to199/pdf/nte128.pdf

The pinout on both is the same (view in fixed font or M\$ Notepad):

Base
_
/o\
Emitter(o o) Collector/Case
\_/

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

The NTE website is really good for quickly finding transistor pinouts.
They're also handy if you need a repair or engineering part today.
They have retail outlets in many repair shops and depots, which means
that frequently you can just drive down the road and get your part
within an hour. Great stuff.

Good luck
Chris

P

#### PeteS

Jan 1, 1970
0
Then do what we do and head for a manufacturer's site.

For example, http://www.microsemi.com/ has both of them (go to the site
and put in the part number in the part number search box) and
eventually you'll get a pretty picture or pdf you can download showing
you the pin description,

Note that I chose microsemi at random - those transistors used to be
made by everyone+dog. Philips, OnSemi (nee Motorola SPS) will have them
to name but another two.

Cheers
PeteS

J

#### Joe Norton

Jan 1, 1970
0
Thanks, that gave me the info I needed. I've got my circuit working.
Thanks to you all.

Joe.

J

#### John Fields

Jan 1, 1970
0
I have two transistors. One is a 2N2219 A and the other is a 2N2905 A.
Both have round metal cases with a tag at the edge. One pin seems to be
connected to the case. Does this help? Please excuse my ignorance!

---
With the leads pointing at you, the lead closest to the tab is the
emitter then, moving clockwise , the next lead is the base and the
next the collector.

I believe the collector is supposed to be internally connected to the
case.

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