CPI Tube issues

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NECRAT
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Re: CPI Tube issues

Post by NECRAT » Mon Mar 17, 2014 5:07 pm

BigRed wrote:Speaking of IOT problems and crowbar circuits I seem to remember a service bulletin from some transmitter company or the other (don't remember if it was Comark, or

The tube was junk, instantly though, but that doesn't sound like what you're dealing with.
They actually do have the SB regarding the crowbar efficiency test. You can do the wire test, or the super secret, not good for the weak, grounding bar test too.
However, I tested this crowbar system every couple of months as part of my periodic testing, and fortunately I had about a month prior to this failure.

The tube is actually holding with some current now, so it is looking more and more like it was a buildup inside the tube. I hope tomorrow to get it close to 800ma.
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Re: CPI Tube issues

Post by NECRAT » Fri Mar 21, 2014 9:10 am

Well so much for that.

The tube crowbarred itself out at -6db, and isn't drawing half the current it did prior to the change at -7db, and the gain and beam current have dropped significantly.

This is looking more and more now like it is cathode poisoning based on this behavior. (Minus the draw of ion current, which is an anomaly. There is always a slight change the ion current detection is bad, and it is really drawing some.)
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Re: CPI Tube issues

Post by NECRAT » Sun Mar 30, 2014 12:51 pm

As of yesterday, the magic tube is now running at 20% with just over 10 watts of drive and 800ma of beam current.

No crowbar events either.
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Re: CPI Tube issues

Post by kkiddkkidd » Mon Mar 31, 2014 6:22 pm

Reading all this, I am ever so glad that I decided to stick with radio...
--
Kevin C. Kidd CSRE/AMD
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Re: CPI Tube issues

Post by NECRAT » Sat May 24, 2014 5:08 pm

Wow I have slacken off on this thread. Through a very slow painstaking process of slowly heating the tube and bring RF into it, day by day, a little more at a time. It got most of the way, fired off again. Restarted. Process restarted itself. Day by day.

I am very happy to say the tube is officially "back on the air" as of a few days ago, running at 90%. It has run this with 4 days. CPI is now convinced this was classic cathode poisoning.

I need to get about 5-6 months out of the tube until I can replace it, but as an engineer, it's always fun to see your patience pay off.
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Re: CPI Tube issues

Post by grich » Sat May 24, 2014 10:23 pm

Congrats...may your weeks ahead be BOOM! free... :mrgreen:

I do NOT miss IOT's. Or the crowbar circuits in the Harris Sigma line cabinets. BOOM!

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Re: CPI Tube issues

Post by NECRAT » Sun May 25, 2014 4:34 pm

grich wrote:Congrats...may your weeks ahead be BOOM! free... :mrgreen:

I do NOT miss IOT's. Or the crowbar circuits in the Harris Sigma line cabinets. BOOM!
I've heard horror stories about the Crowbar systems in the Harris Sigmas...
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Re: CPI Tube issues

Post by NECRAT » Wed Apr 13, 2016 5:15 pm

Just an update to this old thread. The problematic tube was replaced last week. A brand new shiny tube went in and is performing how I would expect it to.

The unreliable tube is on my bench for show n' tell.
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Re: CPI Tube issues

Post by Kelly » Thu Apr 14, 2016 7:34 am

What was the final hour count before finally swapping it out?
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Re: CPI Tube issues

Post by NECRAT » Thu Apr 14, 2016 6:10 pm

I will let you know tomorrow when I return to the shop. The cabinet hours had lapsed at some point, so the hours have to be calculated.

I believe it was close to 70k hours.
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