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Post by Casethecorvetteman on May 20, 2015 1:09:21 GMT -5
Dont you have a set of 9" NEC tubes there?
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Deleted
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Post by Deleted on May 20, 2015 2:01:35 GMT -5
Great! How does the spotkill and I sense signal go to the Nec? Is that compatible? The spot kill seems to be compatible, I sense isn't looking hard either, the biggest problem is that there is a gain (contrast) trim pin on the XG neckboards, that is not present in the VNB, and I really don't want to poke with analog multipliers in this project. Ok looked at the schematics you posted. I think you meen the contrast controll on green that seems to be there for greyscale calibration. That is done on the Marquee vim. I wonder how bad it is to not have drive correction for green. Mostly green is left on default and blue and red are adjusted. |
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Post by gjaky on May 20, 2015 10:18:29 GMT -5
Dont you have a set of 9" NEC tubes there? Yes, I wanted one, but in the end my price offer and the seller expectation didn't meet... |
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Post by gjaky on May 20, 2015 10:24:02 GMT -5
The spot kill seems to be compatible, I sense isn't looking hard either, the biggest problem is that there is a gain (contrast) trim pin on the XG neckboards, that is not present in the VNB, and I really don't want to poke with analog multipliers in this project. Ok looked at the schematics you posted. I think you meen the contrast controll on green that seems to be there for greyscale calibration. That is done on the Marquee vim. I wonder how bad it is to not have drive correction for green. Mostly green is left on default and blue and red are adjusted. No, it's not the "gamma correction", there is real a contrast control on the XG neckboards, on all of them. But there is also one on the input board too, I just don't know yet which is part of the normal menu-driven contrast loop, and which is part of the auto greyscale loop. |
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Post by mastertech on May 20, 2015 10:26:39 GMT -5
Dont you have a set of 9" NEC tubes there? Yes, I wanted one, but in the end my price offer and the seller expectation didn't meet... I would think you would want a burnt tube for testing purposes. Should be almost free except for shipping. |
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Post by gjaky on May 20, 2015 14:19:49 GMT -5
Well my XG is currently up on the ceiling, I don't feel like putting in a burnt tube while it is up there... but honestly I don't even want to pull it down. A whole spare machine would do a better job.
My plan is to measure the already working machine in and out and taylor the VNB according to it on the bench. The spot kill signal on both machines are active high inputs, so they seem to be pin compatible, I don't see much risk in this part.
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Post by mastertech on May 20, 2015 14:26:04 GMT -5
That was going to be my next question, what chassis were you going to use so we can start looking over schematics to see what's what. You need to find a complete machine. Nothing over there? Burnt XG's are free here.
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Post by gjaky on May 21, 2015 0:17:21 GMT -5
I'm not even sure XGs were originally sold here, I only know three XGs here, all was imported from Germany (including mine). Grab something steady: in fact there is an XG751 up for sale here, generating the common sync issue, which is pronounced in the ad, 4500 like hours, no tube pictures, the seller asks 430USD, a year ago I offered him 290 USD (!!!) but he refused, the good thing is it is still up for sale...  I have an XG1351, so that is the main target... |
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Post by Casethecorvetteman on May 21, 2015 5:36:34 GMT -5
$430 is a bit rich
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Post by gjaky on May 26, 2015 13:45:39 GMT -5
Small update:
The VDC power supply being the prototype modell had a small problem, namely the supply lines weren't symmetrical 85 vs. 75 or adjusted 90/80, so upon Scott's idea I put a series regulator on the higher line to drop about 10V, and cranked up the adjust pot so I ended up with 85V/83V (that is 90V/83V without the series regulator, the difference growed with the higher output what I didn't count on), but this will be just as good.
As for the XG spare, the seller of the above mentioned XG asked me today if I am still interested in his machine, of course I now lowered my offer as well, but decided to only buy it if the tubes show minimal to no wear (might have some resell value along with the lenses) AND if it has good (=high bandwidth capable) neckboards. Now if I buy the the XG as a spare, that would mean it has normally working neckboards which would doubt the validity of the Marquee VNB project right away.
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Post by mastertech on May 27, 2015 11:54:49 GMT -5
Now if I buy the the XG as a spare, that would mean it has normally working neckboards which would doubt the validity of the Marquee VNB project right away. Hmmm, keep us updated as to what you decide. I was curious to see what the Marquee neckboard would do on the XG. |
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Post by gjaky on May 27, 2015 12:49:05 GMT -5
Now if I buy the the XG as a spare, that would mean it has normally working neckboards which would doubt the validity of the Marquee VNB project right away. Hmmm, keep us updated as to what you decide. I was curious to see what the Marquee neckboard would do on the XG. I have little hope that the machine meets my requirements, the guy seemed to agree on my offer -still expensive though, but I figured if the tubes are nice I can resell them along with the lenses so I could regain most of the money and I'd have a full set of boards for relatively little money (compared to what would it cost to ship a single board from USA). I'll check out the machine either friday or saturday, maybe in the end of the day he will beg to me to bring it away  The biggest problem so far with the VNB is the lack of contrast control now. One wicked idea would be to connect a JFET (or maybe a BJT) paralell with R12 acting as a variable resistor, there would be needed some biasing network of course, but the two main concerns are a.) how the thermal drift would affect the gain (=color balance) b.) adjusting R12 inherently affects the frequency response of U2 being a current feedback opamp, the outcome is unpredictable, it might turn out to be working or might be a complete failure (= losing bandwidth)  |
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Post by gjaky on May 29, 2015 14:19:53 GMT -5
So today I went to check out the XG751, I was surprised (and sad) to see that this machine also showed the low bandwidth just like the 5 neckboards I have here, although it did not show the "bleeding colors" effect I had on the others. The green tube is 7 at top (R/B: 9/8), but the wear is large and even enough to reuse. The final price seems to be $210. Right now the only thing that is motivating me somwhat the fact it has a few STK393-220s in it which is otherwise hard to find if one fails. I'll ask my friend if he is interested in the tubes for ~$100, if I can sell the lens for ~$50 that would make it still a good deal for me. It seems the Marquee VNB project rocks on! |
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Post by Casethecorvetteman on May 29, 2015 17:12:59 GMT -5
Did you ever try feeding the video signal direct to the neck board to see what results that gave you?
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Post by gjaky on May 29, 2015 17:41:03 GMT -5
Did you ever try feeding the video signal direct to the neck board to see what results that gave you? Yes I already did this, it was the same result. again I've pretty much measured through the boards I have here, even compared them with the PG xtra neckboards, with oscilloscope. Tried to cross feed the signal between the boards (preamplified on the XG board, but the output stage was on the PG xtra board). All test showed without doubt that the XG board eats the bandwidth, in every configuration, while the PG xtra board does not. One thing I try tomorrow: I got out one CXA1709 out of the XG neckboard (this is the preamplifier ic) on which I measured poorer result than it is promised in its datasheet. Just for fun I almost finished a breadboard test circuit to check if it is the IC itself or the PCB board material that is used on the original XG board that sucks. I guess it will be the PCB, because the VPJ13s also performing poorer, moreover putting in the VPA13 (which was doing high bw on PG xtra board earlier) instead of the VPJ13 produced poor results too. The only efficient way to solve this to fit the VNBs in which is a better design anyway. |
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