#76
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Very interesting, Pete! How does the comparison look on a gray scale now?
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#77
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It seems the gray scale is a bit contaminated because the color control will not kill it completely, and so I don't have a recent shot. I will have to confirm this w/a scope, however, and try for one Monday morning. Last weekend, channel 13 ran pledge programming during their usual color bars. Hopefully they'll have raised enough $ to go back to color bars this weekend.
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#78
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Automatic balck level and white balance
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Now it would be real neat to design a circuit that would adjust black level and white balance for a 15GP22 in a similar fashion found in today's modern TV sets. During the blacker than black and peak white pulses within the blanking periods the gun current for red, blue, and green would be individually compared to a reference and then G1 and G2 adjustments made automatically! |
#79
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At this point, if you adjust the G2 for a lower gray and view the set in subdued light the CT-100 picture compares favorably with a digital set tuned to the same analog broadcast. There are differences of course: at those times when the digital set shows virtually no phosphor glow, the same area on the CT-100 screen will sometimes show a very dim glow. On a similar note, I’m borrowing a virtual multimeter. Hope to be able to develop a data-logger-type monitor that will keep a txt file record of circuit voltage. I’d kinda like to learn something about how critical the 115-Vac line-voltage spec is to optimum CT-100 operation. If it works I’d particularly like to gather data on how the high voltage varies with line voltage. |
#80
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The value of remanufacturing vintage parts...
The last of my three vertical convergence transformers failed. One is used in a CTC2, the CT-100 chassis. Sunday morning June 18, 2006, the fuse protecting the H-V cage blew on turn-on. Unlike my two other failed transformers, however, which still display correct dc resistance, this failure wiped out the secondary. The tap is completely open. There are about 12 Meg between the top and bottom of the secondary where about 12 k-ohms should be. This part has an extremely high failure rate. Probably second only to the 'white' peaking coils that rot open.
For the repair, I tacked in one of John Folsom’s newly manufactured replacements I've had for about a year now. It was static-tested at about 4 kV across primary-to-secondary for a few hours when it arrived last June, and so I expected a no-issue installation. On the bench, the H-V ran a steady 21 kV with the new transformer in place and the H-V control set wide open with a 115-Vac line. The focus voltage, which passes through the secondary and is the reason for all the stress on the transformer, is steady at 3.5 to 4 kV, depending on the focus control position. Picture is of the new transformer on the rear of the H-V cage. In the future, I’ll remove the failed core from the transformer housing and use the original case around the new transformer. Returned the chassis to the cabinet today, cranked the H-V control back to the specified 19.5 kV and while I haven’t reconverged it yet, it's perfectly watchable. Last edited by Pete Deksnis; 06-19-2006 at 08:48 PM. |
Audiokarma |
#81
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Nice clean new-looking seleniums there, and may I add a nice clean chassis overall! Are those seleniums new? I've never had to change any on a CTC-2. On the subject of reproduced CT-100 stuff, has anyone made focus and convergence pots? I've had a couple of them with open convergence pots, and one with an arcing focus pot.
Charles |
#82
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Quote:
As you know, the failure of a vertical convergence transformer is particularly insidious because a common failure mode causes a chain reaction that burns out the focus pot. Too much focus current is drawn if the secondary shorts to ground; the 1X2B focus rectifier plate goes cherry, and the pot can literally blister on the outside and melt internally. While its design voltage rating is unknown to me, the focus pot is the center of a three-element voltage divider with nearly 4 kV at the wiper. While I haven’t had to do it yet, I’ve seen an ordinary linear taper pot successfully substituted for the original one. Personally, if I have to do that someday, I’ll make sure there’s an insulated knob on the shaft before I adjust it. I had a pleasant surprise when the chassis came out of the cabinet. Notice in the picture the hue control -- the variable cap on the end of the center shaft of the three running back from the front panel. It's in the dead-center position. Exactly where it was after aligning the chrome AFC a year ago. |
#83
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UPDATE to "The value of remanufacturing vintage parts..."
Finally got to perform a full convergence on the set two days ago, and the newly manufactured vertical convergence transformer is doing a fine job. The procedure improved convergence to the point where the overall 15GP22 image -- to use the vernacular of the streets -- looks sharp as a gnat's ass.
A minor inconvenience is the weather. Yesterday is the second time in recent history that a spell of humid weather affected the high voltage. Not certain where the damn humidity planted the unwanted load, but it's highly unlikely that the new transformer is a factor. The last time this happened was a week after replacing the transformer. A three-week hiatus with no power applied to the set brought it back: the high voltage recovered after the weather turned dry. Last edited by Pete Deksnis; 08-29-2006 at 02:42 PM. |
#84
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Re the low H-V problem...
What with the remnants of the hurricane passing through here recently, there's been so much rain the grass is so green it looks fake. So what better time to again check H-V under extended high-humidity conditions.
Last night I did it a little differently. With a 115-Vac line I pulled open the H-V lead then applied power. The H-V swung right up to 21 kV (about right for a CT-100 unloaded H-V supply) and stayed there. Plugged the CRT back in and powered up again. Sure enough, after some mild frying the H-V settled at a slightly low 17.5 kV, but in a few minutes was back up to 19.5 kV. I believe in my case the culprit is leakage from the flange; last year after restoration I had to remove and cleane the CRT and rubber insulator around the flange to arrest the same frying/leakage. If you have to you have to. But not looking forward to pulling the CRT for another cleaning. Not so much for the work involved, but I don't like potentially messing up a satisfactory alignment. |
#85
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In the case of a CT-100, you could turn the bulb & fan on the day before you plan to run the set. Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10 |
Audiokarma |
#86
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Quote:
David |
#87
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The light bulb/Fan trick basically raises the temp high enough to reduce condensate from forming on surfaces inside the TV. Another approach would be to place a tray of silica gel or drierite (CaSO4) inside the set for a day or so.
I'm 5 miles for the Ocean in San Diego. Even at this distance I'm careful about exposed high voltage anodes outside when the humidity > 60%. Of course, warm humid days and cool nights often leaves the air saturated causing dew to form on cooler surfaces - hence the possibility of arcing. |
#88
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Humidity and what to do next...
For three days now the set has been working w/o H-V problems, but if/when it happens to lose adequate H-V due to weather/humidity again, I'll remount the CRT without the mu metal shield and H-V insulating wrap. Should help pinpoint just where the short is taking place.
Two or three times a year I get to climb up on the roof after a major storm and reorient my $10 antenna towards NYC again, like yesterday. See photo. My humidity problem comes from the lake across the street, which runs three blocks down to the Atlantic ocean, which is of course the real culprit. |
#89
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Hey Pete,
Certainly looks like state of the art equipment. I hope you're not using a $10.00 ladder to get up there. My brother swore he would kill me the next time I climbed on the roof to fool with an antenna. So either way there is risk involved. Be careful. -Steve D.
__________________
Please visit my CT-100, CTC-5, vintage color tv site: http://www.wtv-zone.com/Stevetek/ |
#90
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Quote:
As Pierre Salinger quipped years ago, when quizzed by a reporter who asked if he were safe skating on a frozen pond:" I may be plucky, but I'm not stupid." Actually, I had to crop the bejesus out of that cell picture to get it to load up into AudioKarma's guts (my access to Photoshop is temporarily down). The full frame shows a flat roof. Plus there's an easy-access hatch from the third floor ceiling, with a built-in wall ladder. My son was up there too to keep an eye on the old man. [Fodder for conspiracy theory threads. Much later, Salinger, press secretary to presidents Kennedy and Johnson, got into hot water in '96 for publicly arguing that it was not a 'spark' in a fuel tank that brought down TWA flight 800... ] |
Audiokarma |
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