i guess i just don't know how to use a breadboard

[jlullo]

hey guys...

i have germanium transistors i want to check for gain and leakage. i just want to check them....  is that too much to ask for??

i've breadboarded this circuit countless number of times and i can't get it to work:
http://www.geofex.com/Article_Folders/ffselect.htm

i have the power supply and the leads on the dmm reversed because i am trying to check NPN transistors.

i have it set up like this: (sorry for the crude drawing)


R1 is 2.2M
R2 2.47k

i have the red lead of my DMM on the side of the 2.47 resistor that is going to the power supply, and the black one going to the other lead.


is this correct?

[Mark F]

Obvious question: did you reverse the polarity of the battery? If so, your DMM leads look to be oriented properly. What does the matter seem to be? What voltage readings are you getting?

[jlullo]

mark,
i'm using a powered breadboard.... i have +9v running to the red buss strip , and COM running to the blue buss strip.  is this right?

are the components on the board laid out correctly?

[jlullo]

is there anyone that can help with this?

[Meanderthal]

 Ya know, I keep saying I'm gonna build this little setup...

Yeah, you did it right... I can't see any reason it wouldn't work... unless the breadboard is a bit worn and not making contact or something.

[Mark F]

As Meanderthal stated, you have it layed out correctly. What readings are you getting ? Like Meanderthasl said, if the BB is worn you may not be getting good contact. It's been a while since I've used mine but I remember it being pretty straight forward

[jlullo]

alright.... i reset this up, and think that i actually had the resistors swapped, and i now have the transistor oriented correctly.... i think that i'm getting somewhere right now.  just have a few more questions...

i'm using these formulas...
"I put the switch off, and I check the voltage in Volts. I call this value Voff. Then, I put the switch on, and I check the voltage in Volts. I call this value Von. So the formulas are:
- gain = (Von - Voff) * 100
- leakage (µA) = (Voff / 2472) * 1000000"

on this particular tranny (2n1304), with the switch in the up position, i'm getting 0.09.  in the down position, i'm getting 0.52.  Is the "down" position considered "Von" or "Voff"?

[Mark F]

According to your diagram, when the paddle of the switch is "down" it is the ON position and "up" is OFF

[jlullo]

GREAT.... it's working!!

thanks boys.

i love you.  You all saved my sanity.

[jlullo]

td

[jlullo]

i tested about 6 devices so far using these formulas, and all the leakage i'm getting is around 30... this doesn't seem like a very likely number, does it?

[GonzoFonts]

You may still have something wrong with your setup - post a new pic.

GF

[Mark F]

You may just have lucked out. I remember quite awhile ago I acquired some germs from some old equipment and they all had quite low leakage BUT they all also had quite low gain. Then again, you may just be doing something wrong. Try it with a silicon tranny or two or four & see if you get leakage in the same numbers. If you do then you are more than likely doing something wrong or have something wired incorrectly.

[jlullo]

thanks for the info again, guys...

i'll check out the situation when i get home, take a picture and report back to you.

just to be sure, i should be measuring these on 20v on my dmm and not 2, right?

[Mark F]

thanks for the info again, guys...

i'll check out the situation when i get home, take a picture and report back to you.

just to be sure, i should be measuring these on 20v on my dmm and not 2, right?

If you are only measuring millivolts you will get a more accurate reading on the 2 Volt scale. Measuring across R2 (2.47K) should only be Millivolts.

[jlullo]

there we go... that would be the problem then    i'll take another crack at it!

thanks mark and gonzo!

man, i have to get my prefixes down 

[jlullo]

alright guys......this is what i have for you.

i came home and popped a 2n2222 tranny on the breadboard.  beforehand, i measured it on my DMM, and i got 224 hfe.  on my breadboard, with my toggle in the down position, i get a reading of 1.69 and 0 in the "up" position.  this would mean that i have 169 hfe and 0 leakage.  is the drop in hfe because of the resistors?

in the same scenario, i'm taking a 2n1304 ge tranny.  i plug it in my dmm (which i know is not accurate, because of leakage), but just for reference, i'm getting an hfe of 194.  putting that on my breadboard, i'm getting a reading of .854 in the "down" position.  On the up, i got .056 .  this would mean that i have a hfe of 79.8 and leakage of 22.  this is roughly the leakage i've gotten from the whole bag of 20 trannys.  am i doing this correctly?  could i possibly have germanium transistors that are all between 20 and 30 in leakage?

[jlullo]

i have another scenario for you. 

I'm using another 2n1304 tranny.  I plugged it into my DMM, and got a reading of 173 hfe.  I know that DMM's can't calculate leakage, but do they calculate the correct gain?
I put the same transistor on my breadboard.  in the Von position, i'm getting .70.  in Voff, i'm getting .04.  This would give me 64 hfe, and leakage of 16 ma.  I don't understand.... this must mean that there is something wrong with my test setup, right?

this is driving me so crazy, because i have a creampie board all populated EXCEPT for the transistor.  i have a pile of NPN ge's and i can't do anything with them until i get this down.

[Mark F]

 The readings you got for the 2N2222 look to be O.K. That was the whole reason for checking a silicon tranny, they shouldn't show any leakage. The Hfe looked to be within the proper range. You may want to try a few other sil. trannies & check the data sheets for them to compare. I don't know what the Creampie wants for specs but I would try your Germs & see how it sounds. The Germ tester you have on the Bread Board seems OK

[jlullo]

mark,
so then i take it that since the dmm doesn't check for leakage, it's hfe is way off from what it really is.  right?

if so, then i think i'm in business..

jonathan