Just do a simple CAP replacement first and se if youi get a better performance. Make DAMn sure you use the exact same values. Don't copnfuse .0033 with .033, etc.
hi maybe let the tube bake for a while or try rejuventaing it...connecting g1 and cathode to 220v mains with a 15w lightbulb in series has worked for me before, now i have a crt tester/rejuvenator...i know they dont make miracles but a crt with just a little bit of emission sometimes can produce a watchable picture... cheers
If this has been basically any other TV I probably would've gone farther, but between the cabinet which was in pieces and had to be glued back together (and parts of it are still maimed, such as where someone drilled a hole to mount a replacement power switch, and they also drilled a hole through the metal front grill to mount a replacement speaker), the cabinet collapse had damaged a coil on one of the boards, and the dead CRT I decided this one wasn't worth it. Despite the other damage if this had been the 6 volt version of the tube I might have continued but the 2 volt versions (which I verified this tube is the 2 volt version) are known bad CRTs. If you're interested in one of my more recent videos I did get a Hoffman Easy Vision TV with a weak CRT watchable in the dark
@@bss1250 i was now reading a schematic for a german set that i am currently working on and on this set the cathode is actually more positive than g1...brightness control is from g1 to b+ and the connection to ground only acts as voltage divider...the modulation is also fed on the cathode... are you sure that grounding the cathode will bias the tube hard?or you would be doing the opposite way...my predicta also shows a very dim raster if i disconnect the video wire your eht could also be low contributing to low brightness...but the spark you drawn with the screwdriver looked healthy to me i also have a predicta but its an italian version,the chassis is different and so is component layout and schematic i subscribed to watch your other videos, i also have some videos about my tvs if you want to watch
@Hugo B. I went back and checked the schematic, and the arrangement seems very similar to what you describe. Are you saying the return path for the high voltage is actually to B+ and not to ground? If that is the case I'm surprised it arced to ground as readily as it did, if ground is a high resistance return path. Either way you definitely gave me something to think about, I may get back into this in the future and try it with the brightness pot back in circuit instead of going straight to ground
@@bss1250 The high voltage at the anode is not supposed to return to the cathode...that would cause flashover and destruction of the electron gun like it happens on gassy tubes....you would see a blue glow inside...also if you could ground the EHT it loads down the flyback and it drops to almost zero....i cant explain it with scientific detail because i am no expert but the high voltage is there just to accelerate the electrons that leave the cathode and the faster they hit the phosphor the brighter it gets...something like that...the high voltage will arc to anything close to it that has a more earthy potential,even b+lines.... you dont need to ground the screwdriver for eht to arc to it..however you may feel it depending on the screwdriver you use :) then you have the other grids wich are for focus and they are just there to electrostatically center the electron beam i can only talk for certain about my sets but i believe your predicta would work the same way! there are sets with positive going or negative going video modulation...and some sets feed modulation to the cathode and some feed it to the grid...(the vast majority feeds it to the cathode) ,along with the modulation there is always a dc component in order to bias the tube....i believe all crts have to biased the same way so just try feeding the cathode with about 20 to 30v more dc than on g1 , that should bias the tube in a way that it produces a nice bright raster..also you need to check voltage at g1... if your schematic doesnt list voltages you can check the tube's datasheet...but often its just bad potentiometers... when you said in the video that you did not know wich way around are the controls , on the Philcos i believe the horzontal hold pot has a shielded cable to it, identifying that can help you figure out easily wich one is for the brightness... Also on many of my tv's turning the contrast all the way down kills the raster so that might be a problem also. edit: just looked at your video and g1 is marked zero volts on the schematic and cathode 35volts so yes a 20 or 30v difference like i said above and the cathode is more positive than g1...i really believe that the ground point on your brightness pot is for voltage dividing. i would check those two voltages at the neck of the tube...the other grids dont really matter because they are used for the focus.you have 400v boost voltage on one of them and you can select from 0 to 200 and something on the other, whatever gives the best focus
the filter choke you mentioned after the video amp is just a video peaking coil and you can bypass it if its open...its just a copper coil wound around a resistor making a certain inductance..bypassing it makes some artifacts in the image but no big deal. also if capacitor c24 is leaky you will have excessive DC voltage at the cathode because it will go around the brightness pot making the image brighter, i dont know if excessive voltage can overload the tube and make it cut off, maybe it can...100v like you read there seems excessive to me in respect to a 0v g1... i would also check the EHT, i believe that 15kv must give you a 1cm steady arc...those eht rectifiers like to go weak
I have one of these in my basement. Always wanted to restore it. It has everything it worked when I first got it Thirty years ago.
Just do a simple CAP replacement first and se if youi get a better performance. Make DAMn sure you use the exact same values. Don't copnfuse .0033 with .033, etc.
hi
maybe let the tube bake for a while or try rejuventaing it...connecting g1 and cathode to 220v mains with a 15w lightbulb in series has worked for me before, now i have a crt tester/rejuvenator...i know they dont make miracles but a crt with just a little bit of emission sometimes can produce a watchable picture... cheers
If this has been basically any other TV I probably would've gone farther, but between the cabinet which was in pieces and had to be glued back together (and parts of it are still maimed, such as where someone drilled a hole to mount a replacement power switch, and they also drilled a hole through the metal front grill to mount a replacement speaker), the cabinet collapse had damaged a coil on one of the boards, and the dead CRT I decided this one wasn't worth it. Despite the other damage if this had been the 6 volt version of the tube I might have continued but the 2 volt versions (which I verified this tube is the 2 volt version) are known bad CRTs. If you're interested in one of my more recent videos I did get a Hoffman Easy Vision TV with a weak CRT watchable in the dark
@@bss1250 i was now reading a schematic for a german set that i am currently working on and on this set the cathode is actually more positive than g1...brightness control is from g1 to b+ and the connection to ground only acts as voltage divider...the modulation is also fed on the cathode... are you sure that grounding the cathode will bias the tube hard?or you would be doing the opposite way...my predicta also shows a very dim raster if i disconnect the video wire
your eht could also be low contributing to low brightness...but the spark you drawn with the screwdriver looked healthy to me
i also have a predicta but its an italian version,the chassis is different and so is component layout and schematic
i subscribed to watch your other videos, i also have some videos about my tvs if you want to watch
@Hugo B. I went back and checked the schematic, and the arrangement seems very similar to what you describe. Are you saying the return path for the high voltage is actually to B+ and not to ground? If that is the case I'm surprised it arced to ground as readily as it did, if ground is a high resistance return path. Either way you definitely gave me something to think about, I may get back into this in the future and try it with the brightness pot back in circuit instead of going straight to ground
@@bss1250 The high voltage at the anode is not supposed to return to the cathode...that would cause flashover and destruction of the electron gun like it happens on gassy tubes....you would see a blue glow inside...also if you could ground the EHT it loads down the flyback and it drops to almost zero....i cant explain it with scientific detail because i am no expert but the high voltage is there just to accelerate the electrons that leave the cathode and the faster they hit the phosphor the brighter it gets...something like that...the high voltage will arc to anything close to it that has a more earthy potential,even b+lines.... you dont need to ground the screwdriver for eht to arc to it..however you may feel it depending on the screwdriver you use :) then you have the other grids wich are for focus and they are just there to electrostatically center the electron beam
i can only talk for certain about my sets but i believe your predicta would work the same way! there are sets with positive going or negative going video modulation...and some sets feed modulation to the cathode and some feed it to the grid...(the vast majority feeds it to the cathode) ,along with the modulation there is always a dc component in order to bias the tube....i believe all crts have to biased the same way so just try feeding the cathode with about 20 to 30v more dc than on g1 , that should bias the tube in a way that it produces a nice bright raster..also you need to check voltage at g1... if your schematic doesnt list voltages you can check the tube's datasheet...but often its just bad potentiometers... when you said in the video that you did not know wich way around are the controls , on the Philcos i believe the horzontal hold pot has a shielded cable to it, identifying that can help you figure out easily wich one is for the brightness... Also on many of my tv's turning the contrast all the way down kills the raster so that might be a problem also.
edit:
just looked at your video and g1 is marked zero volts on the schematic and cathode 35volts so yes a 20 or 30v difference like i said above and the cathode is more positive than g1...i really believe that the ground point on your brightness pot is for voltage dividing. i would check those two voltages at the neck of the tube...the other grids dont really matter because they are used for the focus.you have 400v boost voltage on one of them and you can select from 0 to 200 and something on the other, whatever gives the best focus
the filter choke you mentioned after the video amp is just a video peaking coil and you can bypass it if its open...its just a copper coil wound around a resistor making a certain inductance..bypassing it makes some artifacts in the image but no big deal. also if capacitor c24 is leaky you will have excessive DC voltage at the cathode because it will go around the brightness pot making the image brighter, i dont know if excessive voltage can overload the tube and make it cut off, maybe it can...100v like you read there seems excessive to me in respect to a 0v g1... i would also check the EHT, i believe that 15kv must give you a 1cm steady arc...those eht rectifiers like to go weak