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Hi Wolfgang,

Please forgive the capital letters. I am not shouting but I do hope to get your attention to what the other TekScopes experts (Craig Sawyer, Chuck Harris, Tom Jobe) are telling you:
* THERE IS NOTHING WRONG WITH YOUR CURVE TRACER!!!!
* YOUR FINE PHOTOGRAPHS SHOW A PERFECTLY NORMAL SET OF 2N3055 CURVES ON A 577.
No matter how much you think your photos show your curve tracer is not working it is working perfectly.

Just in case that was not clear let me say it a little differently:
* YOUR 577 IS WORKING EXACTLY LIKE ALL OF THE 575s, 576s, AND 577s I HAVE EVER USED (I OWN 5 AND I HAVE USED MORE THAN 20).

There are several things that are causing this misunderstanding on your part:
* Several of the curve tracer controls interact with each other and/or with the transistor's actual parameters to create misleading (or annoying at best) visual artifacts that you are pointing out as performance defects of the curve tracer such the loops on the left side of each curve. Those are characteristics of the transistor itself. Others have pointed out how to prove this by substituting a small value capacitor for the transistor to see that it creates loops too.
* Your expectation of what ideal transistor curves look like conflicts with 1) how real transistors (with stray capacitances and other ugly details) actually perform; and 2) how real world instruments such as a 577 operate due to limitations of real world circuit designs, or constraints like costs, weight, size, heat, etc.
* Your incorrect expectations of what transistor curves SHOULD look like on a curve tracer are confusing you further and further.
* You don't have enough experience with Tek Curve Tracers to realize that yours is operating perfectly.
* You do not have enough hands-on experience with curve tracers to realize the subtleties of how they operate. For example I have 50+ years of experience with the 575/576/577 and I still haven’t used every capability of these sophisticated instruments.
* The designers of the 576/577 knew it would have to test devices that weren't invented yet. As a result these curve tracers have many more controls and capabilities that they would seem to need. Until you need these capabilities those controls only create more confusion if you set them wrong. This is part of your problem.
* There is no blanking on the 575/576/577 so you see the unusual traces between steps at the right side of each step in your photos. This is because you were using the FAST Step Rate. I could explain why this is so but it would be better if you learned why yourself (from the Theory of Operation" section in the Service Manual) so you would realize it is not a sign that there is something wrong.

Regardless of what "wrong" curves you get on your 577, if you provide a photo, we can explain why the curves look that way. It will either be due to:
1) The settings of the curve tracer (such as using the FAST Step Rate),
2) The way the curve tracer circuitry works (it doesn't use blanking),
3) A real world transistor is not the same as an ideal transistor (Miller Effect, leakage, etc).

If I succeeded in reassuring you that your curve tracer is working properly, CONGRATULATIONS!
On the other hand, if Craig, Chuck, Tom, and I haven't convinced you, then I suggest you sell the curve tracer. You will never be happy with it and you are going to waste a lot of time and money chasing a chimera.

My only request is that you think about how much time we have spent so far explaining to you that there is nothing wrong before you ask us for further reassurance. It won't be a good use of our time.

I hope you are able to stop worrying and begin to enjoy the remarkable instrument you have. You can download a copy of the Tek book "Semiconductor Device Measurements" (link below) to learn how to use your curve tracer to make all sorts of device measurements. If you look carefully you will see the steps have loops in some of the photographs in this book.


Dennis Tillman W7PF