Re: tunnel diodes retrace lines in curve tracer

Kurt Rosenfeld

There is a straightforward modification to a 576 to get it to display the full tunnel diode curve. I did this a couple of years ago when I was measuring a bunch of tunnel diodes. The fixture gets a shunt resistance. The resistance of the shunt should be small enough to keep the parallel combination of the shunt and the negative resistance of the tunnel diode positive at all points in the curve. An opamp measures the voltage on the diode and applies a proportional offset current to the vertical amplifier inside the 576. The offset cancels the current in the shunt resistor so that the displayed current is just the diode's current. The modification was completely reversible. As I recall, the only reason the side cover had to be removed was to hook a clip lead (or maybe two leads) to a particular point in the vertical amplifier. There was no soldering involved. I removed the clip lead when the measurements were done. If I can find my notes from that, I will scan them and share.

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