B&K 501A Curve Tracer Question (2024)

I've attached two pics from my curve tracer that has had me confused for a very long time.
I'm hoping someone here that is much smarter than I can shed some light on what I'm seeing.
The traces are from a MJ15003 NPN transistor.
Depending on how hard I drive the transistor I get the different traces.
If I drive the transistor hard I get nice straight traces.
If I drive the transistor lightly I get a trace where a person see's a retrace line???? Not sure how to describe it. (Triangular trace)
On the one pic it looks like one line is missing, but that is just in the pic. I have all 5 lines on the scope.
Scope Trace 2 is the trace of the transistor being driven hard.

So my question is, do I have something wrong with my B&K curve tracer?
Or is this normal?

I'm hoping someone can help me understand what I'm seeing.

When testing transistors that won't fit into the provided sockets, be sure to keep the connecting lead length as short as physically possible to minimize the effects of stray signal pickup and possible oscillation.
Many of the socket adapters used on lab grade curve tracers were fully shielded and incorporated ferrite beads on the transistor socket leads to minimize these effects.
If indeed you find that reducing the lead length solves or at least reduces the problem, you might want to construct a compact socket adapter for TO-3 and TO-66 transistors on a small piece if perf board that plugs directly into the banana jacks.

- Jim

On the signal transistor, what do you get w/ sweep voltage at 20 and steps at 10, 5 or 2 uA? May need to change v scale on the scope.

Regards,

Dewey

If the traces do not change, the explanation can be found in the manual (link below). BK sez it is either excessive collector capacitance/inductance or high temp. See pages 26-27 of the PDF, which is pages 20-21 of the manual.

https://bama.edebris.com/download/b&k/501a/501a.pdf" -="window.open(this.href);return false;

Regards,

Dewey

watchmaker wrote:If the traces do not change, the explanation can be found in the manual (link below). BK sez it is either excessive collector capacitance/inductance or high temp. See pages 26-27 of the PDF, which is pages 20-21 of the manual.

https://bama.edebris.com/download/b&k/501a/501a.pdf" -="window.open(this.href);return false;

Regards,

Dewey

Thanks for your response.
I'm guessing this is normal since they talk about it in the manual.
It is probably the capacitance/inductance since I saw the curved displays as soon as power was applied...
I had read that in the manual way back when.
Thanx for reminding me!!

Eugene

And I get it on both my analog and digital scopes on some transistors. So I would say what you are seeing is an accurate trace and is normal.

Regards,

Dewey