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Old 21st October 2012, 12:46 PM   #291
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The steps on the grid drive do not look correct, they have to be completely flat. Right now you have a tri level on each step. The small level difference near the top of the plated drive would certainly cause a loop. Also the phase is off, this will also add to it.
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Old 21st October 2012, 11:25 PM   #292
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Quote:
Originally Posted by avincenty View Post
The steps on the grid drive do not look correct, they have to be completely flat. Right now you have a tri level on each step. The small level difference near the top of the plated drive would certainly cause a loop. Also the phase is off, this will also add to it.
Ok, I will try and clean it up, are you using coax cable to the grid? I am using a thin stranded cable only...

Jaz
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Old 22nd October 2012, 12:37 AM   #293
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I do not use coax. From what i can see from your previous picture it appears those level differences are not random, as if there is an issue either with your primary clock or the counter.
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Old 22nd October 2012, 06:41 AM   #294
mogliaa is offline mogliaa  United Kingdom
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Isolate the counter from the rest of the circuit and measure clock signal there. I don't use coax either and my clock was very clean even in a breadboard. Twist grid signal cable with ground signal in a twisted pair to the socket. I added a ferrite bead as well.
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Old 22nd October 2012, 07:51 AM   #295
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Guys,

Thanks for the feedback, I won't have a chance to work on the project for a few weeks due to my travel schedule, will get back to it once I get back, I think it is getting pretty close.

Jaz
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Old 28th October 2012, 09:59 AM   #296
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Had some free time on my road trip, so I was going over some of the pictures that I took of the tracer and noticed that the plate voltage and staircase waveforms are not like the way Merlin showed in his design. In his version (top graph in the attach picture), the peaks occur at the step transitions, but in mine they occur in the valleys, would that result in the double traces, I wonder?

Ale, if you can show me a shot of the waveform at the gate of the IRF9630 that would be great, since my design closely follows yours. Really like to get it working once I return from the road, and start to trace some curves!

TIA,
Jaz

Click the image to open in full size.
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Old 28th October 2012, 03:35 PM   #297
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The stairs still do not look correct. Is the channel ac coupled or dc coupled? It should be DC coupled and the steps have to look completely flat. If the slant in the picture is real, it would cause the loop as the grid voltage is not the same at the same plate voltage, yielding a different plate current.
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Old 28th October 2012, 03:45 PM   #298
mogliaa is offline mogliaa  United Kingdom
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Jaz,
If you're sensing at the ground return as per Merlin's suggestion be careful of the ground loops including your scope when DC coupled. There are some grid-anode signal traces earlier In the thread.
As Alfredo says the grid steps should be clean and flat steps!
Ale
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Old 28th October 2012, 10:16 PM   #299
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The steps were DC-coupled I believe, I will double-check... Ground loop is a real possibility as well, appreciate the pointers as usual.

Thanks,
Jaz
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Old 31st October 2012, 10:18 PM   #300
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Default Almost there...

Made some modifications to the gate drive circuit and managed to get rid of most of the loops, still not quite a straight line yet though, I also found that there is severe line interference during "business hours", I think the construction site down the street really mess up the AC grid somehow... So I can only run the tests either early morning or late at night

Another thing, my current setup is completely exposed - basically no shielding, I am sure that also contributes to the "dirty lines", going to try and put it in a metal box to see that would improve things. Slowly getting there...

The latest curves:
Click the image to open in full size.

Jaz
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