#181
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Absolutely stunning cabinet and electronic restoration on this set. The screenshots are the best I’ve seen to date on a 15GP22. I was thinking a 3D printer for the knob as well.
Late to the game on this thread, don’t know how I missed it.
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#182
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Are sure you weren't looking at Nick's screen caps?
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tvontheporch.com |
#183
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The screen caps in post #150 look pretty decent to me...
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#184
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Those screen caps were not very bright when I took those a couple of years ago. Always have needed to run this set quite dark to get enough red.
Today, I took a quick shot during the Super Bowl. This is the west coast, so there was still significant light coming into the room from the window at 5 PM or when I took the shot. As you can see, red is decent. I'll take some nicer screen shots after I've had a chance to fine tune things better. Noting the concerns about positive grid voltage and grid current mentioned above, I made an update to the circuit by adding two 1N4148 diodes in series between the red grid and cathode. I used 1N4148 to have fairly high speed diodes. Two in series since they are only good for 75 V reverse voltage each. This limits the grid to only +1.2 V on positive peaks of the video. Here's the circuit: With this circuit, the DC restorer sets the black level ahead of the cathode follower, and the diodes clip the peaks off the video drive to the CRT grid. I'm pleasantly surprised that clipping the positive peaks still lets plenty of red drive through (so I don't really need the strongly positive peaks on the grid signals). I compared this to the original to reconfirm that this was all doing some good. The difference is very compelling. Without the cathode follower, the DC restorer isn't able to keep the black level fixed on the red gun any time the red signal becomes large. As reported above and on the last page, grid current competes with the action of the DC restorer, and the DC restorer loses. Now with the cathode follower and diode clipper, the DC restorer keeps the black level fixed as it should, and I can get decent red. Not like a new tube, but pretty watchable. With the clipper in there, hopefully I am not damaging the red gun. |
#185
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Are you still using the brightener?
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Audiokarma |
#186
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I hadn't seen those caps before (maybe three years ago), they do look good. Please keep us posted on how well the tube holds up. My set can be viewed in moderate light (even blinder-inhibited daylight) but could be much improved by your scheme. I'm just going to leave the burn-in period to you.
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tvontheporch.com |
#187
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Tom, As it happens, I re read your entire post from 2013 yesterday. The set still looks spectacular. Looks like you're still looking for the plastic channel selector insert. Thought about powering up my CT-100 for a Super Bowl photo but got caught up in the game. Also on the west coast and a lot of light streaming in from my west facing windows.
-Steve D.
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Please visit my CT-100, CTC-5, vintage color tv site: http://www.wtv-zone.com/Stevetek/ |
#188
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Yes, the brightener is still on there. I'll try it again soon without just to compare, but I have a hunch it needs to be there.
That's quite a reading assignment you gave yourself! Thanks for the nice comments. Still a work in progress, trying to get this tired old CRT to give us a nicer picture than it wants to. |
#189
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Quote:
Last edited by timmy; 02-06-2018 at 06:31 AM. |
#190
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Quote:
http://www.videokarma.org/archive/in.../t-258583.html Look near the end of the page for how they work. . |
Audiokarma |
#191
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Quote:
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#192
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Made some further progress on the CT-100 after some time away from it. Two key findings:
1. I actually get more red with the red screen turned DOWN, not up. I modified the circuitry to lower the voltage range of the screen controls, and this actually helped. I don't understand why this is the case. Anyone have an understanding of how the screen control is behaving this way? I've confirmed that the voltage at the CRT socket goes up and down with the screen control setting as expected. 2. While building the cathode follower into the chassis more permanently, I happened to spot check some components under the chassis, and found the choke on the plate of the Q synchronous detector was open. I'm sure I checked this coil when I first restored the chassis a few years ago, but undoubtedly this coil opened in the mean time. This was confusing my interpretation of what was going on with the red. I'm surprised at how well the color worked with this choke open, but it's certainly much better now. Also replaced some drifted resistors while I had it on the bench. Not a bad idea to pull the chassis on a set like this every few years to catch the newly deteriorated components. I've now got the cathode follower built in to the chassis, hiding inside the cage where the selenium rectifiers once resided. This leaves the chassis looking relatively original. The cathode follower is worth its weight in gold for enhancing the red on this set. It's officially "daytime watchable" now, which makes it a lot more fun to have around. Here are some daytime viewing pictures. Blinds are closed (with sun directly on the windows, which still lets a lot of light into the room). Here are some quick screen shots. Didn't have nice reds like these in the daytime until now. |
#193
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Quote:
This also provides a bit of hope to anyone with a rather anemic looking 15GP22, provided of course it's still under vacuum. |
#194
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Really looking nice. I think if you took some closeup shots in the dark the images would look spectacular.
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#195
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These are simply quick shots with my iPhone. I guess I got a little lucky with the lighting level. I didn't have to adjust the brightness up or down from normal viewing for those shots.
Quote:
Anyone have any idea why I'm seeing the screen voltage behavior I mention above (red is stronger at low screen voltage, not higher)? I wonder if the higher screen voltage is throwing off the purity? Wouldn't really seem to make sense that it is actually lowering the emission... |
Audiokarma |
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