Re: Infamous D180 is it good or bad.


Hey Ernesto,

Most aren’t that bad. It is this particular TD Tek part number 152-0329-00 that is why it is so expensive. The end goal is to repair a 284 which has a rise time of less then 70 pS. I have had this one on the shelf for a while before I trusted myself to not damage it more then it is already not working. My main need was to check if the TD was working to know if that was the failure mode or if more trouble shooting was needed. If the TD had been bad it would have been more then I paid for the 284 to replace it. Due to the incredible rise time this particular diode has an extremely low capacitance only 1.5 pf which is why it is so expensive. Tek them selves only used this TD in I think 2 units. The 284 and I believe there was a sampling time base that had one as well.

But one of the reasons I really like being a member of this group is I always learn WAY more then I expected when I ask a question. As for my use I have found my self calibrating scopes lately 400 series and 7000 series mainframes so a puler is needed. I was looking for a spare if my current TD pulser decided to stop. For the curve tracer *shrugs* I had one that was just repaired so might as well use it. Also from a controllability standpoint it was the least likely to destroy the diode once set up correctly. I did not trust the rigol power supply with this part given some of its output issues. Long story short the need was validation vs experimentation. The part was irreplaceable and I was overly cautious. But I am learning every day.


On 6/8/2020 6:08 PM, Ernesto wrote:
Hi Eric,

I didn't know that a tunnel diode can be so expensive, $250, and why you cannot do your experimenting with a $10 tunnel diode.
Also I am not sure if a curve tracer is necessary for any investigation into a tunnel diode.
Maybe I am ignorant, but I think that all what is needed is to drive the diode along a measured current range (instead of voltage range) and measure the voltages across it.
So, a higher voltage supply with a large resistor plus mA meter in series, and a voltmeter, is all what is needed.
One raises the current, measuring it together with voltages to define the positive resistance curve until the peak,
then one measures the positive voltage jump over the negative resistance region, and the current if it changed.
then one comes back down in current until the voltage jumps back over the negative resistance region to the flank of the initial positive resistance curve.
Who cares what happens in the negative resistance region, unless you want to build an oscillator instead of a fast comparator?

Or am I too simplistic?


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