I used to wonder how they measured current when set 📐 up in x-y mode

So I just accepted it 

So now I think they are just showing voltage. (Ya think ?!?!?  )

And yeah isn't that what oscilloscopes do 

I don't know the complete details I think the volts per division is set to "make it right" I'll see how it's done when I actually do this.  (Eek  )

So what's all the fuss about well in my book 📖 I'm working through the have a sections where students use a Tektronix 575.  I would love to have one but I looked at some and they are big and heavy, have lots of tubes (huh?!?) and $$$$ 

Dont get me wrong I would love to have one 

Now credit to the book 📚 they have instructions how to monitor Ic on the scope which is cool.

Seems like I saw on MEF one of the members here posted some beautiful pics of output characteristic curves 

Ok thought I would wrap this one up.  Last set of experiments were same setup only now an emitter resistor was added. 

This was the first time I couldn't notice a trend maybe I should compare with the other configurations idk I'm still like a mindless zombie doing this stuff.

Anyhow wow an emitter with a resistor wiped out the tpi3055

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Ok I did notice something seems this was the first time base current took a hit.   

Excellent point sir thanks nice to hear from you.   

I know right now (I think) that all of this is gonna go together like a big 🗝� key lime pie I'm lust learning how to make the crust and missing the key ingredients 

Thank you very much sir that was awesome 

And the results are in with some conclusions
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When a small hFE transistor was placed in the circuit the voltage drop across the collector resistor was very small or very low collector current

When a large hFE transistor was placed in circuit there was a big voltage drop across the collector resistor ie much greater collector current

Meanwhile...base current remained pretty much constant

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So I'm thinking that the base is like a rock.  In response to that I was gonna post Bob Seger like a rock...but I really like fire lake.


(I've been to Cold Lake but not Fire Lake)

Some eye opening results after some transistor testing 

I needed two NPN transistors
-one with lower beta/hFE than 2n3904 (hFE 173)
- one with higher

So I started testing and the first victim mps222A tested hFE 175 

So next I pull out this billy badass radio shack TO-220 TIP 3055.  I'm like oh hell yeah it's on now 
It tested 11 hFE.    retested and got 12 

Tested ecg128 and get a 171....ok keep going 

So I had about ten of these puny 2n3391a and wow  tested hFE 419 


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Now obviously I'm lacking comprehension here I'm sure there is a reason for this and it should make sense.

Anyhow I have my test candidates 

Anyhow I think I was supposed to draw a conclusion after doing another experiment.

I set up another circuit this time with two variable resistors.  First I adjusted VR2 until Vcc was 12V then I had to adjust VR1 until Vce was 9V.  Then take measurements.  After that adjust VR2 so that Vcc was 9V and leave VR1 alone.  Do it again for Vcc at 6V.
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The results
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So...maybe I need to go back and read the chapter text but what I notice is the base current is not affected by the collector voltage. (ya think  )
Oh wait a minute....neither is collector current huh?  Wondering how that is possible 

Now the significance of this concept escapes me at the moment

I presume this is a big deal so I will ponder it for a while.

 

Thank you sir you are so right I use to work so many problems crunching numbers applying formulas finding theta and crap and was getting nowhere  then I would dream about being in a time machine and going back to university like in 1973 where they had a rigorous lab class.  Then I found these books by Lorne MacDonald that were like a lab class telling me to do stuff 

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Each chapter has concepts and examples of problems and calculations then at the end of each chapter are lab exercises and more problems.

 

Yes sir excellent thanks   

So I got to wondering on a TO-220 is the metal tab the same for every transistor in that package?

This gets further convoluted because seems like I remember some voltage regulators in that package 📦 and the metal tab possibly being ground.  Like when you guys fixed my audition chorus 

Then seems like I remember on TO-3 packages like the metal output transistors (I'm not cheating and looking while typing this so hope I am right but the metal case is the collector?)

Hence why people have to use mica insulators and stuff.

So back to the TO-220 I'm off to see if the metal tab
-is always the same thing
-or no 

And oh yeah obviously the metal tab with a hole in it is for attaching to a heat sink but don't necessarily assume a heat sink is ground 

At the end of the day I guess the best thing to do is just make sure what stuff is before connecting or soldering or placing in service.

Since this post is already a rambling stream of consciousness I'll add that I guess the white paste is not an electric insulator it is there to conduct heat and aid in heat transfer 

Which brings me to dielectric grease how many years did I put this on spark plugs and stuff not knowing why it's just what I am supposed to do.

Seems like I should know if it conducts or insulates electricity.   

That is a great article thanks

 

I just took a brief inventory of what's on hand.  I guess I just need to jump in and start testing

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I'm almost to the part in the lab exercises where I'm supposed to do a lot of the same stuff except with a 2n3053 and 2n3055 to see the results of smaller and larger beta.

I have some TO-39 just not 2n3053 and then heck I could buy some 2n3055s but idk how to connect a TO-3 to a breadboard 

Not that it would be impossible but I think I may start checking stuff that I have lying around and try to find some suitable candidates.

I did look up Hfe vs Beta and saw a reference to common emitter circuit but I'm not there yet.

Maybe I can measure Hfe of 2n3904 then try to get a transistor that has lower and greater (they need to be NPN as well)

Quote from: g1 on May 04, 2025, 01:28:19 PM

Quote from: saturated on May 03, 2025, 02:28:35 PMTurns out that a variable resistor turned all the way to zero is a dead short 


fortunately my power supply kicked to zero 

Did you connect the supply to something other than the diagram in the picture?

We have a winner.  No sir pretty sure I messed up and had a lead from the node connected to the middle terminal (I think)

Instead of terminals one and three (10k at all times)