Re: Infamous D180 is it good or bad.


Eric
 

Hi Dennis,

I checked the curve tracer this morning. Vc was 6.5V 8K series resister, vertical was 0.05 V/Div. Horizontal was 5uA/Div My confusion is I am not getting the typical curve that I have seen with tunnel diodes and a curve tracer. I took a picture this morning of the curve tracer. I had horizontal magnification turned on. This is right around 10mA as measured on the meter. I do now see the gap in the diode. Does the curve look somewhat strange because this one is just so fast. Also if the collector is increased just a little more the diode just turns ON and stops switching. I would test a few more to see if they all behaved the same however I have a sample size of exactly one. From the reading I have done and my lack of understand I am leaning towards this is a good diode and my problems with the 284 are bias related.

Photo has been posted here

https://groups.io/g/TekScopes/album?id=248216

Eric

On 6/7/2020 3:17 AM, Dennis Tillman W7pF wrote:
Hi Eric,
Download a short article on line about how tunnel diodes work and you will be able to tell from the pattern on the curve tracer how to confirm it is working and you can actually measure several important TD parameters. The negative resistance region of the TD is not something Tek curve tracers handle very well so you will probably see something like oscillation on the trace. That is OK.

The TD will go to 4 different points on the CRT as the voltage and current changes around the area where the negative resistance is.

The collector voltage setting should be on the lowest position of your curve tracer (6V on a 577). The horizontal volts/Div should be set at its lowest setting (50mV/Div on a 577). The vertical current should be set to 2mA/Div if you have a 10mA TD. The series resistor should be fairly low like 120 ohms on my 577. These settings will get you in the ball park.

Very slowly increase the collector voltage. As you reach 50mV the collector current may have already reached 9mA. If it has you should start over. If it hasn't yet reached 9ma then continue increasing the voltage towards 100mV. At some point, the current which has been rising in almost a straight line will slow down then stop rising. That point marks the peak current or Ip. This is an important parameter to document. You should also make note of the voltage at the peak current. That is the peak voltage or Vp. If you attempt to increase the voltage beyond this point the tunnel diode enters its negative resistance region where it drives the curve tracer crazy. The tunnel diode will suddenly shift a few hundred mV to the right and the current will drop by up to half. It is now in a new stable location. Don't bother to increase the voltage any further. To find out everything else you need to know you have to start reducing the voltage very slowly. As you do this the current will begin to drop. At a certain point the current will slow down and stop dropping. This may be around 1mA. This is the valley current or Iv for your TD. The voltage at that point is Vv or valley voltage. If you reduce the voltage a bit more the TD will now jump again. This time it will be almost right back where you started. It may be 1mA up on the curve and you started at 0mA but that is not important. You are at the point where you can begin the entire cycle all over again. Now you have Ip, Vp, Iv, and Vv so you can calculate the approximate negative resistance of your TD. Rtd = (Vp - Vv) / (Ip - Iv).

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Eric
Sent: Saturday, June 06, 2020 6:15 PM
To: TekScopes@groups.io
Subject: [TekScopes] Infamous D180 is it good or bad.

I have a Tek 284 that I am working on what is mostly working there is just some issues with the pulser output of course. I finally worked up the nerve tonight to test the Diode it has been on the shelf for a while. I knew these didoes were fragile and are very expensive to replace. I found them… for $250.00 each diode. So the way I have things set up, a curve tracer set to DC and very sensitive measurements. I have the collector going out to a Keithly 6500 to watch the current. As I turn up the collector I get current flow in to the diode. At about 9mA there is a LARGE increase in current. But NOT a short. If I dial down the collector it looks like the diode recovers. RIGHT about 9 mA I can get it to flutter between the 2 current readings. So if I am reading the instruments correctly is this tunnel diode good? I am thinking it is but I am very new to tunnel diodes. I know I am in the deep end of the pool with this one but confirming the diode would be great news to getting this 284 up and running. I can put up a short video if it will make more scene

Eric




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