Matching Transistor Problems

[lcstier]

I have built the transistor testing circuit in the intermediate book on page 11, however I am having a problem. As the circuit is pictured I can only get approx. 50 to 90 mAmps when testing a transistor. If I decrease the 27k ohm resistor to a 5.6k ohm the mAmps will be approx. 140 to 180 mAmps. This is with the potentiometer set at 0 ohms on both tests. If I add any resistance on the potentiometer the mAmp draw will decrease. I am testing TIP31 transistors. I would like to get closer to the testing procedures as I can, 250 mAmps to start the test. I built the circuit on a breadboard twice just to make sure I didn’t mess up, but the results are the same. Any ideas???

[John_Koorn]

lcstier,

Try testing MJL21194 transistors instead of the TIP31. I think the circuit is designed for the MJL21194. With other transistors you may be getting different results to what is expected.

John K.

[Forrest]

Hi All, Just read thru the entire intermediate handbook and have a question. I know up until this book was published that we used the HFE portion of the multimeter to test and match the transisitors. Is there any advantage of using the tester JB used as described in the book over the HFE test?

Bud

[Tom C]

Hi All, Just read thru the entire intermediate handbook and have a question. I know up until this book was published that we used the HFE portion of the multimeter to test and match the transisitors. Is there any advantage of using the tester JB used as described in the book over the HFE test?

Bud

Yes, it provides more current to the base to full open the transistor. the "opening" is not linear, you want to see what the transistor does when it is hit enough current to fully open it.

Tom C

[Yves7772]

Hi,
first I have to say that I use the circuit in the Bedini SG intermediate book, page 11.
I built the circuit today, I tested MJL21194G transistors.
I had to replace the pot and the 27k resistor with a 62ohms to get .103A on the ampmeter. I have bougth 30 of those transistors and they all performed almost exactly the same from .102 to .104A. I have also tested a 2N3055 in the cirduit and the 2N3055 give around the same result.
I have rebuilt the circuit twice and it give me same result.

I have search the forum about this topic and I did't find a lot of info to help me.
Am I on the right thread to talk about that ?

Yves

[D Rhodes]

I tested just 6 previously used transistors. mjl 21194's on a tester I got on ebay. Does the result mean none are matched? Or is it close enough?
# hFE uf mV
1 21 633
2 25 644
3 23 633
4 27 638
5 25 623
6 25 643

[James Milner]

Tom,
I take it without having the book in front of me that you run 250mA through the base and match on that basis?
Is there any value in using smaller variable resistors on the base so as to match the transistors in situ on the board and in operation?
Is it possible to tune the individual base resistances so that mismatched transistors can be used?
I'm thinking in terms of locations where even getting a MJL is difficult let alone 100's in order to match them.
Thanks for your advice
James

[Tom C]

That sounds about right for the base current. I don't remember exactly what mine is set at. I have never done what you are suggesting it should be possible. You would have to tune your circuit to the lowest transistor you have. If you need marched ones we sell em.
Tom C

[James Milner]

Thanks Tom,
Got plenty of matched ones, just wanting to plan ahead and achieve the best tuning possible.

[Forrest]

Hi lcstier,

I had the same problem when constructing mine as well. Had to change some things around. Now it works great. Check out my old threat on this.

http://www.energyscienceforum.com/be...iate-book.html

Bud