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  #46  
Old 01-11-2014, 03:21 PM
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What you are describing is an effect of macrovision copy guard. You can buy boxes on ebay that can be connected between a DVD player (or VCR) and an external RF modulator that will remove the macrovision signal from the video.
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  #47  
Old 01-11-2014, 08:14 PM
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Tubejunke Tubejunke is offline
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I want to see if I can simplify this cathode current thing and test my own understanding at the same time. An electron tube in it's most common form is a triode or three section tube. I am using the triode for the sake of simplicity. There is a cathode circuit, a plate circuit, and a control grid circuit. So, given three sections there are three circuits involved in order to bias (provide a difference of potential or voltage) each of the sections.

So, if we were to want to measure the current flowing through any of these sections, we would have to break the circuit, and I don't think that it would matter where except within the tube its self which would be impossible. Once the circuit is broken, an amp meter would need to be connected in series. I must stress the fact that the meter must be IN SERIES, like part of one of the wires more or less, NOT parallel!!!

With all this being said, we should now be able to tell how much current is running through the circuit with no problem. So, in order to create a remote test port you would simply extend one of the wires feeding the cathode portion of the tube to an easily accessable location and create a method of easily breaking the wire and ineerting the meter. Then you want to be able to easily reverse the procedure and remove the meter, then provide a good re connection.

I am thinking that when designing this the best idea for me at least would be to install a glass fuse holder. Remove the fuse, perform the test, then reinsert the fuse. The fuse will provide protection from over-current so you won't need to worry about it anymore.

If you want to get really fancy, you could do the fuse holder AND a stand alone analog (or digital) milli-ampere meter. They can probably be found for sale on Ebay or possibly even some electronics supplier. A final thought for me is the use of an industrial motor over-current device, basically a breaker with a switch knob. Nice and reliable and you never buy fuses, but probably not cost effective.

So maybe this will help some as there has been some confusion on what to do here and it is a rather important issue from all I have ever read or heard. I don't have a schematic to elaborate on pin #s or any of that. I hope also that my take on this is correct.
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  #48  
Old 01-11-2014, 08:23 PM
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The probable reason to measure the cathode current versus current at other elements is that adding a meter in the cathode circuit would be least likely to affect the circuit operation. With all of the other work done on one of these sets, temporarily unsoldering the cathode connection and using a couple of clip leads should not be too tricky, at least it was not for me.
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  #49  
Old 01-12-2014, 12:08 AM
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I don't understand why manufactures didn't simply put a small value cathode resistor on the horizontal output. It would tend to drop the current a bit and add an element of safety, besides making it a simple matter to measure voltage drop across the resistor. Would that create linearity issues, or what am I missing?
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  #50  
Old 01-12-2014, 02:36 AM
kramden66 kramden66 is offline
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never trust old electrolytics , I was running the set figured I'd finish up with the convergence , the picture shrunk and I shut it off , I was thinking something got in the set and was shorting , nothing , turned it back on , after a minute it shrunk and the breaker popped , I then poked around to see if any wires were messed up , I checked the power rectifiers and one was shot , I then checked the old electrolytic and it was hot , must have taken the power rectifier out , so even 15 minutes later it was warm , so now to replace it and the rectifier.

earlier I tried the cathode and I couldn't get readings on the meter , the set should have produced a picture and it didn't ,I will try again with the 10 amp input of the meter but if that doesn't work I don't have anything to check the cathode.
also checked the anode and it is running about 22k , I will recheck that once I get the set running again , I guess if its 22k and not 23 it will be ok , if it runs under 22k is that harder on anything ?.

mike
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  #51  
Old 01-12-2014, 12:24 PM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by kramden66 View Post
...earlier I tried the cathode and I couldn't get readings on the meter , the set should have produced a picture and it didn't ,I will try again with the 10 amp input of the meter but if that doesn't work I don't have anything to check the cathode.
Doesn't your meter have a lower range, e.g., 500 ma (1/2 amp)?
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  #52  
Old 01-12-2014, 08:27 PM
kramden66 kramden66 is offline
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what if i was to put a resistor 1 ohm or less between the cathode and ground , I could measure the ma that way , I have .39 ohm 10 watt resistors wasting away I could add to try it

mike
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  #53  
Old 01-13-2014, 12:54 AM
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Is your meter a digital readout or an old fashioned needle type readout? DMMs tend freakout and give nonsense readings when fed the high frequency non-sinusoidal current pulses of a HO Tube cathode. If you don't have an analog meeter Radio Shack has a relatively cheap one that I've found to work decently in measuring cathode current in these sets.
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  #54  
Old 01-13-2014, 02:24 PM
kramden66 kramden66 is offline
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digital meter , I don't have any analog or a vtm
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  #55  
Old 01-14-2014, 02:45 AM
kramden66 kramden66 is offline
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Well I put a 1n4007 in and it seems ok , also put a replacement for the electrolytic, I did accidently break the tip off the circuit breaker and changed it but the one I put in is rated at 1.75 , the one that was in it was 5amp , will the 1.75 be ok or will it trip ? I calculated the watts divided by volts and got 2.6 , the set is 310 watts , I tried a couple times a start up and it came on ok with the 1.75 , I even tried turning a set on one the same line to see if the momentary surge would cause anything , I almost plugged the vaccum in to see if that surge would do anything but didn't, so will it run and trip after a while because it is too low ?
now to try to get the ma measured on the cathode , get the sound tuned up a little and take some pics to post.

mike

Last edited by kramden66; 01-14-2014 at 02:56 AM.
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  #56  
Old 01-15-2014, 10:49 PM
kramden66 kramden66 is offline
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I tried to get a cathode ma reading using a .39 ohm resistor between the cathode and ground , the set came on but I still got no readings on the meter , so I decided to remove the .47 capacitor to see what it would do then I got readings , so I removed the resistor and just hooked the meter up between the cathode and ground , I was getting 220 to 222 ma and thought that's a little high , so I turned the horz lin till I got to 200ma , the sams instructions say no higher then 210ma and the schematic says 200ma , so I put it to 200ma , it will drift a little to 201 or 202 and sometimes to 199 but mostly hangs at 200 , it does shoot up to about 225 or so on start up but quickly drops to 200ma, the fly is just luke warm so it is not running as hot as it was , the anode is 22kv area with very little change when you turn the brightness up or down , so looks like its running ok , I will know better when I adjust the vert height and lin for a more uniform circle , my only fear is what if the lin is off and the only way to correct it so it is more uniform is to increase the ma ? I wont know till I do more with it on Thursday , now I just have to tweak the sound to get rid of a little buzzing and it looks like it is going to be ready for viewing.
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  #57  
Old 01-16-2014, 03:40 AM
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As a rule of thumb the lowest you can get the horizontal current without objectionably affecting the horizontal linearity is usually the safest setting for the fly to run at, though it should probably be fine as you have it now.
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  #58  
Old 01-20-2014, 02:25 AM
kramden66 kramden66 is offline
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Well I got it up and running , fixed the sound issues , convergence is as close as it will get , it could use a degaussing but I don't have one , I will try to find a junk tv and take it out and use it to wave around the screen and slowly pull back , I did do the wire to the chassis from the cathode for future readings, the record player fan is a good idea , its quiet and keeps air moving inside even though its not rapid like a cooling fan but that would make noise.

I will post pictures as soon as I get them taken .
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  #59  
Old 01-20-2014, 09:12 PM
kramden66 kramden66 is offline
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here are the pics , the colors look better in person , I do have an issue maybe someone knows what to do , when fade to black the picture gets bright , also when for example and explosion in a scne in voyage happens the flas of the explosion causes the image to go darker for a second while the flash of the explosion occurs , is this the video out tube ? I played with agc and it didn't seem to make a change.

mike
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  #60  
Old 01-20-2014, 10:02 PM
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Looks good ! As for the brightness and explosions, There is a lot said here about sets with and without DC restoration to the picture tube biasing. It effects light and dark pictures, where they tend to drift off where they should be.... I can't say I have seen it so you should look to someone who has seen it.... But it's an idea, and some sets without DC restoration have strange brightness issues...

Could even be HV regulation issues..
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