PNP or NPN

[momo]

I dont know why I did not think of this before but my dad is a retired service technician for a cable company and guess what, I asked him if he had some old trannys laying around.... I just got a box full! like 30/40 trannys.
The thing is there are alot of the metal canisters trannys with no indication on it, so what would be the best method in finding out if they are PNP or NPN without blowing them all!
I am building R.G's PNP tranny testor and will test them all once I know how to seperate the 2 differences.
thanks!

[R.G.]

Set your DMM to the lowest resistance range. It may have a diode range.

Use it on a diode with anode and cathode marked so you know which lead is + and which is - when in resistance setting. Most have the red lead + and the black lead - , but it's critical to KNOW before testing the devices.

Once you know which DMM lead is +, use the DMM to find out which of the three leads conduct which direction to the others. For the purposes of this test, an NPN looks like two diodes with the anodes connected together. A PNP looks like two diodes with the cathodes tied together. You get no conduction any other ways.

It should sort them out pretty quickly.

Then your next question will be how to identify collector from emitter, yes?

[momo]

R.G, thanks alot for your time! I read everything you write on any post and all your replies are always pertinent,If I can get to your level.... anyway so yea correct me if im wrong but I think the little tab on the canister points to the emmitor.

Oh and I have the Radioshack auto range dmm with one selection for resistance...

[petemoore]

  I put a transistor checker socket in my DMM's transistor checker socket.
 [makes it easier to test the tranny's, my DMM's socket contacts are too deep...
 Stuff the can legs into the DMM's transistor Hfe tester.
 All different ways, I'd start with PNP like
 Collector
               '>' Base
 Emitter
 Often the pattern used where the leads come out of the bottom forms a three point 'arrow'.
 Basically it's just trial and error...hit or miss with a three pin/three hole puzzle..you're looking for a 'normal' hfe reading, something probably between 20hfe [mostly unusable transistor except as diode] and 200hfe [maybe more].
 Then you can do a Base/Emitter diode threshold voltage test, using the DMM's diode checker, look for a Ge diode in the transistor, or, if you get a B/E diode threshold voltage reading that looks more like a Silicon Diode...it probably is a silicon diode...in and Si transistor.
 Could be you found a clutch of dinosaur eggs in a basket. If they are PNP Ge's [and usable], or NPN ge's, you've found some nice 'relics' !!

[momo]

petemoore thanks for the reply, my dmm does not have the tranny inputs to test...

[Mark Hammer]

A DMM with transistor hfe testing can be bought for so little these days (I saw one for $10 in Princess Auto the other day), that you owe it to yourself to get one.  BY all means, learn what can be learned from RG's sugegsted exercise, but for convenience' sake, get a meter with transistor testing.  EXTREMELY useful.  There are voltage and current ranges on my meter that in my lifetime I will never use as much as I use the transistor test function in a month.

[momo]

Yeah, your right I have to upgrade a couple things since I got this new habit!.I recently bought a new 25w weller, I thought thats watt I had ,but it turns out it was a cheap copy...what a difference that made!, I will never kill anymore cts pots trying to solder to ground...and so yea, a decent meter I think now is required.

[Meanderthal]

I got this new habit

Ah yes, another fume sniffer...  They say it ain't good for ya. But whadda 'they' know.

[momo]

Ha!, talking about fumes...I just finished canibalizing two boards from 2 extremes, part of a Apple computer board that I took from a roadside throwaway and a 60's Bogen all transistor radio!

Well the fumes from the Apple board are real bad! quite nasty and nothing like I,ve had before the Bogen was like the familiar usual, quite good