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  #1  
Old 12-30-2014, 04:37 PM
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ctc12 clone beam current

hey all, how would i check beam current on a 63 ctc12 clone chassis. im trying to rule out a possible bad crt in my silvertone set being i still cannot get good hv regulation after all has been checked more then twice, and or subbed.
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Old 12-31-2014, 06:41 AM
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It's called a CRT tester, if you don't have one buy one. But the CRT has nothing to do with HV regulation, I'd look elsewhere.
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Old 12-31-2014, 07:37 AM
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there is something to be said about this beam current because from what i have gotten here is that if the beam current is to high it will somehow prevent the regulator from working correctly. if its high the hv will be low, and thats what i have and refuses to regulate in the proper way that it was designed to do. the hv and beam current is said that it works together . as for the crt tester, i have 3 of them.
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Old 12-31-2014, 12:00 PM
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You could measure the beam current by inserting an ammeter in series with the CRT cathode connections. On a CTC12, I would disconnect all 3 cathodes from the chassis, then connect them all to the red cathode output on the chassis via an ammeter. The total beam current when the picture starts to bloom should equal the regulator current with a black screen.
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Old 12-31-2014, 12:52 PM
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ok i had checked the hv current with dark screen hv adjust low and got 1.64 ma and the adjust up was 0.93 ma. so to make this set bloom all i have to do is raise the bias alittle with the r g b drives total counter as they are now. just making sure i have the right wires, the cathode, these are the yellow wires ? if this beam current is to high where would the blame be at this point on this chassis ?
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Old 12-31-2014, 06:52 PM
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You're barking up the wrong tree, troubleshooting wise.

Actual beam current is an irrelevant figure as far the the CRT is concerned, but it does matter for the regulator. You don't need to know what beam current is to figure this out. If for example you cannot get a full brightness (and not bloomed) image with the regulator out of the picture and the CRT tests good on a reliable checker, you have an issue on either side of the horizontal output transformer or the transformer itself is cooked. In short, you're not making enough HV to drive the CRT hard enough to work correctly. The giveaway is the blooming- if it's happening before you get normal screen brightness, you don't have enough HV or the supply isn't 'stiff' enough. Aka, it lacks current and you should investigate the oscillator, tubes and flyback. If that's not it the HV rectifier may be weak, the flyback may be past its prime, or you have some serious leakage to deal with somewhere. If it's a smoker set, remove and clean everything with HV on it. Believe me when I say, you will throw up at what comes off...

If on the other hand you can't get full brightness without blooming and you know the horizontal section is good, the CRT is probably gassey enough to cause excess current drain but elude detection on a CRT tester- ask me how I know this is possible...


My guess? You probably have a bad picture tube (gassey), and you need to sub another one to confirm. Appearance of shiney getters is not a reliable indication the tube hasn't gone gassey- again, ask me how I know. You need to be methodical about eliminating one thing at a time, or you'll never find the problem. I'll give you a hint- you only need just over 1ma to get a decent picture with north of 20kv on the CRT.
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Old 12-31-2014, 10:02 PM
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Don't rule out a bad HV rectifier. Also, if there is a current limiting resistor for the HV rectifier filament, check it as its resistance may have gone up.
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Old 01-01-2015, 03:37 AM
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If you pull the CRT socket and the HV comes up and can be controlled properly by the regulator then that may prove a gassy CRT.
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Old 01-01-2015, 08:03 AM
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well ok it all makes sense but this set has a new fly, tried several rectifier tubes, cathode currant 190ma, several regulator tubes, and the rgb drives must be kept counter clock all the way because if i set the drives and having to use the bias alittle to set the drives then normal operation causes blooming and during the blooming the hv dips to sometimes 18-19 kv not enough really bad on white scenes. the brightness is all the way up and it does give a nice picture but it seems with the loss or not enough hv scenes will change color as it blooms. i had watched the hv dip on white scenes and wont go up untill the white changes. this tv was from a non smokers house which is a plus,lol. i have a dvom that checks frequency so is there a way i can check the frequency by probing a specific pin somewhere on the chassis to get an idea what it may be and then again what should the frequency be. the vert holds and the horiz hold is good also if its any indication. all the under chassis caps were changed in and around the horiz section also, nothing i ever done to the set will fix the hv i cant believe i may be missing something here. caps were changed on the vert board never a change for the good. it really is lacking hv and it makes it harder to set it up correctly without enough hv. the lack of enough hv is still unknow to me weather its a bad crt or something else i dont know but would like to get to the bottom of it once and for all. but the brightness is all the way up but its not as bright as it should be because the drives are low because of the lack of hv but even little changes in the scenes will pull the picture in on the right side alittle. if memory serves i think when i took the crt plug off the hv barely made it to the 22-23 kv mark with the adjust maxed clockwise and with the reg cap off the hv climbed to over 30kv. in other posts i had posted a pic of a mark on the crt starting at the anode button extending down the bulb about 6 inches just to the dag on the outside but the mark is inside the bulb where i thought maybe the interior dag was burned off in that area causing these problems but all and all i dont know.

Last edited by timmy; 01-01-2015 at 08:54 AM.
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Old 01-01-2015, 11:21 AM
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Only way to know for sure is run another CRT with this chassis, if things work as they should the CRT is bad.
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Old 01-01-2015, 11:26 AM
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yes it would rule alot of things out as i do have other sets with good crts but would have to take apart 2 sets, oh well...
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Old 01-01-2015, 11:46 AM
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seeing as it takes at most 10 min to pull a chassis on these simple sets, that seems a lot more logical than more test and part changes.
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Old 01-01-2015, 11:50 AM
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yes thats true but with limited room that i have makes it alittle more difficult but ill have to do it. to bad i didnt have a spare in the closet,lol lol. but in the end the sets will have to be set up again when put back together, if only there was a way to tell if there is a gassy problem with this crt i would do it. i tried the crt tester in the cutoff mode and it has been said that if there is gas present it will show something of color in the neck but i have done that already in the dark and nothing there.
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Old 01-01-2015, 12:15 PM
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I am guessing there is gassy as in neck glow purple in which case CRT will not work at all, then there is gassy where CRT just does not perform correct. The way to know for sure is trying the chassis on another known working set. No more need to guess whats wrong. swapping is the way to go.
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Old 01-01-2015, 12:21 PM
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Did you ever check L14 (coil from service switch to cathode leads of crt) that I mentioned many many post and threads ago? if the swap shows the issue is with the chassis and not the CRT I would suggest you check that while the chassis is out.
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