Plan to do this tonight or this weekend possibly this afternoon if I can.
Btw I don't come up with this on my own all credit 💳 goes to the author of the book I'm working out of.
It took me a long time to get to this point where I'm looking at a circuit and actually making the circuit that HAS A TRANSISTOR :dbtu: <3) :tu: so I'm stoked to say the least. This will be my first ever :tu: hopefully one of many.
That said let's get on with it. :grr
A diagram of the circuit I need to make is shown below
IMG_20250502_121541565 (1).jpg
My instructions are to vary VBB until VCE is 6V
by adjusting a variable resistor :trouble
Then measure and or calculate VB, VRC, VRB, IC, IB, Beta, VCB, and VBE
Then after that I do the same with VCE at different values. Investigating linear, saturation, cut-off etc :loco
And a lot different cool stuff.
Here's my victims
IMG_20250502_121553576.jpg
xP
Ok first order of business determine pinout
I wanted to go old skool and pretend it was 1970 and no Internet or peak atlas and no datasheet available :loco
I know it's NPN from the diagram (never points in)
So I just started poking around looking for a base emitter junction then the collector is gonna be the other one.
It looks to me like flat side facing forward the pinout is EBC
IMG_20250502_130618717.jpg
xP
Ok I think I got lucky and spared a slap upside the head by our esteemed member in Tasmania :lmao:
IMG_20250502_132307274 (1).jpg
xP
Alright got it hooked up and adjusted
I couldn't get it to work for a while then I figured out I was missing the ground lead on the third pin of the variable resistor
IMG_20250502_140526076 (1).jpg
So I'm off for some probing and calculating
xP
And that's a wrap (I think until one of our esteemed members finds an error in my calculations :lmao: )
I was frustrated I could not calculate VBB and gave up and measured it :grr
IMG_20250502_142622183.jpg
Btw I will be doing many more of these and will spare you the gory details and pics..unless I find something really cool 😎 to get excited about and run through the streets screaming eureka xP
So thinking out 🔊📢 loud I'm wondering about a few things that I'm gonna investigate
Did I just bias a transistor?
Is Hfe the same as Beta ?
Also I get it this is very simplified but seems in the future I will be encountering base voltage in alternating current.
Also in this experiment seems kinda like a waste all that emitter current going to ground but yeah there is a lot to be revealed later on fortunately.
:loco
Id like to announce a major discovery :dbtu:
Turns out that a variable resistor turned all the way to zero is a dead short :lmao:
fortunately my power supply kicked to zero :tu:
xP
Anyhow I'm back to it same circuit just changing VCE :loco
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 :lmao:
fortunately my power supply kicked to zero :tu:
Did you connect the supply to something other than the diagram in the picture?
Quote from: g1 on May 04, 2025, 01:28:19 PMQuote 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 :lmao:
fortunately my power supply kicked to zero :tu:
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)
:grr
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 xP
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)
I just took a brief inventory of what's on hand. I guess I just need to jump in and start testing
IMG_20250504_183639798 (1).jpg
xP
As far as hfe vs beta, they are the same thing.
Here's a link to a good article on it, note what they say about hfe of circuit. Usually for substitutions we need a beta greater than what the circuit requires. Knowing beta of the transistor does not tell us the circuit gain.
https://www.ovaga.com/blog/transistor/what-is-transistor-hfe
That is a great article thanks
:dbtu:
Congratulations on your experiments.
Nothing beats hands-on.
Most books are old school (transistors were a BIG novelty in the 50s and 60s) so examples are "dated" but all of those have modern equivalents.
For 2N3053 you can use any modern mid power transistor, think cheap and plentiful TIP31C or similar.
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 :grr 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 :lmao:
IMG_20250506_195904015.jpg
Each chapter has concepts and examples of problems and calculations then at the end of each chapter are lab exercises and more problems.
xP
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.
IMG_20250506_194801699.jpg
The results
IMG_20250506_195344111 (1).jpg
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 :lmao: )
Oh wait a minute....neither is collector current huh? Wondering how that is possible :grr
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.
xP
Some eye opening results after some transistor testing :tu:
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 :grr
So next I pull out this billy badass radio shack TO-220 TIP 3055. I'm like oh hell yeah it's on now 8|
It tested 11 hFE. :grr retested and got 12 :loco
Tested ecg128 and get a 171....ok keep going xP
So I had about ten of these puny 2n3391a and wow 8| tested hFE 419 :loco
IMG_20250507_183312016.jpg
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 :tu:
And the results are in with some conclusions
IMG_20250507_193546468.jpg
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
IMG_20250507_193600746.jpg
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)
Vbe looks "like a rock" because it is being force fed throughn am high-ish resistor (100K)
As of the wide Hfe disparity:
small signal (preamp) transistors are optimized for high gain, they don´t worry about high current because they typically will be used around 1-2 mA or so.
Low dissipation also, 300-500mW (tops).
Power transistors on the contrary are optimized for POWER :trouble , high dissipation (70 to 120W), high current (think 10-15 Amperes), etc.
*Everything* in this World is a compromise, so the heavy price paid is abysmal Hfe.
You will find than in all power Amps, power transistors are never used by themselves, *always* driven by a medium power driver transistor, in a Darlington or Quasi Darlington configuration, so their Hfe multiply.
For example my rule of thumb for 50-100W power amps I design is a 2N3055 (Hfe 10 @ 10A) driven by a TIP 31/32 (Hfe 40 @ 1A)) for a combined Hfe of 400, go figure.
I am very conservative (which is safe), in practice combined Hfe is quite higher, but that is a guaranteed minimum value.
Later I switched to power Darlingtons, TIP142/147 (which are a sort of Industry Standard, being also used by Fender Marshall Ampeg Laney Peavey Crate, H&Kettner which should mean something.
Guaranteed Hfe @ 10A is 1000, go figure.
Thank you very much sir that was awesome :dbtu:
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 :tu:
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
IMG_20250509_212526447.jpg
Ok I did notice something seems this was the first time base current took a hit. xP