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.

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.

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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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 ?

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.

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.

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.

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.

Only way to know for sure is run another CRT with this chassis, if things work as they should the CRT is bad.

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...

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.

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.

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.

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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yes i did check L14 the ohms, compaired to the sams. if im correct i didnt cut it from the circuit i just measured the ohms and it was where it should be so i didnt feel i should remove it from the circuit.

the hv stays steady depending on the scene being shown on the screen because white scenes are the worst as during white scenes the hv drops and wont regulate to maintain until the white changes to some other colors. the brightness is always at max, but heres the kicker the blooming is so much worse if i do the grey scale the way it is said to do by putting in service mode and what ever color dont show up i would have to use the bias alittle and adjusting the rgb drives per the sams. this is when the blooming occurs so i have to leave the bias counter and the rgb drives counter in order to get any decent picture, and the white scenes are still a problem setting it up this way. so the result is a somewhat not bright picture although clear its not right. i didnt watch the ma during all of this but this is when it blooms as it seems to when a bigger demand is placed on the crt by raising the drives and or the crt bias, it cannot handle it as it will bloom and pull in on the right side screen. if i turn the brightness down and then turn it back up it does not bloom provided the rgb drives and the bias is fully counter clock.

You have a HV problem, then. Start looking at the horizontal section or HV rectifier.

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Perhaps the HV reg resistors or caps that tested good on low voltage test equipment break down and stop working at rated voltage.

well i already tried a solid state 3a3 rectifier, no difference. i also checked the hv regulator resistors and they checked at 1.6m and 1.59 close enough to 1.5 meg. the funny thing is first getting this set from the beginning the hv was a problem so since then i changed all the caps under the chassis with no change in the hv regulation including the flyback. i thought i found the problem when i changed the fly when i found the focus 1v2 was wired wrong but that didnt help after correcting that. i had thought there was a problem somewhere in the crt drive circuit chroma board or somewhere else affecting the regulation of the hv but im all out of options as to where to look. i was trying to cover as much as possible befor pulling the crt and swapping to rule it out because i am limited to room here and yet the crt in the set tests very good for the age.

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lol,lol, thats just it i dont know anymore whats going on with the set. and yes i have to swap the crt and if another crt does the trick then ill be amazed at what may be wrong with the other seeing as it tests great. but it could be alittle gassy enough to create this problem and that would be a real shame because it does test good.

They can test good and be gassey...

well with my on going hv issue with this set i do have a question. with the set on hv present at anode crt plug off should there be any voltage at any of the crt pins. i checked with a dvom to ground and have no voltage at all except at the focus pin which was 7 volts , would this sound right ? and the hv with the anode wire off the crt is 19kv just at the wire. anode wire back on, crt plug off i was lucky to get 22 kv, thats it, picture scene changes and will dip right down to 19 kv or less. i didnt try another crt yet but was looking around for something concrete here that may give me an idea the crt is finished maybe due to gas. i read an article online about crts and what was said about getters is that a bright shiney mirror like getter is good no air or gas. however what also was said was that a white of course means it took on air but the last was a getter that is coal black no mirror shine at all indicates gas in the tube. has anyone heard of this coal black getter meaning a gassy crt ?

Unless white there is no sure indicator, looking at getthers, of gas.

Well if it's 19kv with no load, you've got a chassis problem. It should shoot up to the setpoint of the shunt regulator and stay there with no CRT attached, does the HV pot do anything in that state?

the hv pot adjust does seem to work but to get even 19kv the pot has to be maxed. there is nothing else i can seem to look at as i looked at what seems to be everything already and have not found anything wrong. so if its a chassis problem then i am overlooking something here. or it is infact the crt. i thought the hv without connected to a crt will be limited because the crt acts like a capacitor so being off the crt 19kv sounds maybe like thats all i would get, i dont know at this point. but then again hooked back up to the crt i would think it would shoot up but didnt. does anyone know the leads that come of the hv regulator tube as to which one if there is a specific lead that does the triggering of the regulation, maybe a specific lead from that tube i can trace if this lead is used as some kind of reference for the hv regulation. because this hv just sits dont raise up just dips as if there were such a wire were cut.

the HV adj should not "seem to work" it should work, in a very linear fashion.

Disconnect the pot from the circuit and confirm (preferably with an analog ohm meter) that it is working as it should (500k to near 0 resistance as you adjust).

Confirm the voltage readings at the shunt tube grid and cathode, make sure the grid varies with the pot.

Confirm the total bias of the shunt tube is within specs of the sams.

At some point I recall you saying the HV would go to 30kv with out the CRT anode attached.

If now you are saying the max is 19kv without the CRT attached then only 3 things can be wrong.


Remember you are working with high voltages all over the place (400v around the cathode and grid of the shunt, 30kv at the anode) so be careful.

1) bad shunt tube

2) bad shunt tube bias

3)no loner getting 30kv with shunt tube disconnected.

this set is nuts, lol, lol, the 30kv was with the shunt tube cap off. i have tried 4 shunt tubes all had the same result , no change. as for the voltages at the shunt tube they were where they should be. and 19kv was with the anode wire off the crt. as well as the currant too was ok. i had unsoldered the pot and checked the ohms and again was good.

lets break it down

all the following with CRT anode off to take the CRT out of it.

shunt cap off
30kv at anode lead

shunt cap on
19kv to 22kv

HV setting to max

so the shunt is drawing current with pot a the max HV setting

two things can cause it to draw excessive current

1)bad shunt tube (gassy/grid emissions), replace with a KNOWN working one.

2)incorrect bias (voltage divider resistors/pot)
leakying cathode/grid cap on shunt tube (upsetting the bias as well).

It has to be one of the above.

Did you alter any wiring around the shunt? does the cathode resistance to ground change the the HV pot?
do you have resistance checks for the tube pins on the shunt.
did you REPLACE the grid to cathode cap on the shunt? if so did you make sure the replacement cap was good?

I wonder if your HV reg tube socket is making proper contact with the tube pins? If not that would explain correct voltage at the socket, but incorrect behavior of the tube.

19kv with the HV pot maxed and the cry disconnected means a shunt regulator problem, does it have one of those 100meg resistors in the circuit somewhere? Might have drifted. You need to take readings of the regulator tube cathode and grid, post them here. The bias on the regulator is certainly funny...it's dragging your HV down for some reason.

ok your right so far but the reg tube i had tried working ones, known working i didnt alter anything at all in the set and the cap i think you are talking about cathode cap i believe it was a disc cap and i got one from moyers but it looked to small even though it was marked as the right one i still had no luck so i found on ebay nos caps and put that one in, was like the original i had changed in the first place. i have the ma specs in earlier posts on the regulator and they appeared ok to a member, it my have been you. you mention voltage divider resistors, where exactly are they? if its the high wattage ones around the hv pot i already did check them. i dont remember if i did resistance checks on the hv reg tube but i do believe i did because i do remember doing all of the others taking awhile to do so.:drool: so i dont think i would have left that one out.

is it possible the wire burned inside the insulation ? if it did then i would pull the wire slightly and if it stretches then that could be it so ill look into that. the pins look very good and the tube fits tight in the socket, but i could check that again.

it has 2- 1.5 meg resistors and i checked them and they drifted very little 1.6 and 1.59 not so bad within range. i already posted the voltage findings:drool: and the ma from all the few wires coming off the 6bk4 reg tube. please check further back on this thread for the voltages they are here. i think there were a brown wire, a green wire and i think a yellow coming off that tube.

I think you should try switching places of those 2 1.5meg ohm resistors......

Turn the horiz centering control.... Does it do anything....? What exactly does it do....?

Turn the focus control, do you have a range on it....? Does it do a lot, or not....?

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A long shot but there is usually a low ohm resistor
in the HV rect filament inside the HV cup. Also if you unplug the CRT
socket does the HV come up ? May have been covered but the thread is
getting long !
And dont forget the H. blanking tube, causes all sorts of odd problems.

73 Zeno:smoke:

the horiz centering control is just about all the way to one side it will swing from one side to another but to center the screen the pot is all the way to one side. the focus does have range although it could be a bit clearer. and the 1.5 meg resistors i was going to try 2- 1 meg resistors but that i think will only kind of change the pot position from maybe maxed to the half mark.