Dumont RA-109A help needed - very little high voltage

[Zenith26kc20]

mighty glad the CRT is good! A quick look at the schematic shows that set to be.... complicated!

[John Folsom]

Clean the glass at the end of the bell between the yoke and where the metal bell attaches to the glass, this should cure you leakage from the metal bell to the yoke.

Use a piece of plastic hollow flexible tubing like a stethoscope. Stick one end in an ear, and use the other end to listen around in the HV cage to find the location of thee HV sizzle. Of course, often you can see it in a dark room.

[kramden66]

Gonna try shortly to see if i can see the hv problem , also paper towel cardboard tubes help in a pinch to locate noises , from what little i could see this set has a great picture , no wonder why its 35 tubes and dumont went out of business.

mike

[kramden66]

can't see or locate the arc , if i move the board where everything is hooked up the sound changes , could be on the other side but tough to see and can't pull the chassis out far enough to look , i guess i could coat everything , whats good and cheap i can apply , a rubber sealent or silicone ?

it may look complicated but everything is spread out so room to work on it.

mike

[John Folsom]

I do not recommend coating to try and resolve HV arcing/corona issues. First identify the actual source/cause of the problem, then you will know how to resolve it. Use the small flexible hollow tube method to locate the actual source. The paper towel cardboard roll is too big and not flexible. You may have to remove HV covers, or pull the chassis to locate it. If you pull the chassis, you will likely need to have the focus coil and yoke hooked up. You need not have the CRT HV hooked up.

[kramden66]

there was a tube shield ( not from this set i don't tink ) it was under the rim of the crt , so that must have been what caused a short through the wood , i moved the yoke back to where its supposed to be and it works but still have to locate the arc issue .

so your saying i can leave the second anode unhooked and run the set ?

[John Folsom]

Yes, just make sure you manage the loose end of the HV lead. I like to tape the end inside a glass container so it is shielded from causing trouble. Running with the lead unhooked is the same as just turning the brightness all the way down, so there should be no issues.

[kramden66]

i haven't had time to try or do anything but read this in the riders tv trouble cures vol one , breakdown between chassis and flyback tranformer lead .. in order to eliminate electrical breakdown between chassis and red/white wire from the fyback the red/white wire to the capacitor end of the clip on v230 ( 1x2 ) is removed and replaced with a white wire to the tube end of the clip on v230 .... perhaps this is my issue ?

mike

[wiseguy]

on my RA-109A I had the same corona/discharge issues, and it was the small doorknob caps for sure, it was a light "tick Tick noise, but enough to bother me so I replaced them
this is my 2nd home dy from suregrey and want was supose to be a 1" cut turned out to be a little of 3".. so now I will watch how I carry heavy things and always ask.!

[kramden66]

Wow hope you feel better soon , i don't have a tick tick i have a rappid sound that causes the image to get in and out of focus and slight chage in brightness and it jitters the image , you can see on the probe the voltage drops and rises , so whatever it is it has moments where it slows and almost stops or just keeps going , i can try replacing the doorknobs again , i have ceramic disc caps that are 470pf at 15kv , i tried them before but that was when the lead was being shorted , now that it is not maybe they are the cause.... btw it looks like i will only have to do a little touch up on the vertical , looks close and the horz might be ok , once i lick this issue it wont require extensive linerty / width issues.. i hope.

mike

[old_coot88]

Originally Posted by kramden66

...i don't have a tick tick i have a rappid sound that causes the image to get in and out of focus and slight chage in brightness and it jitters the image..
mike

What you describe sounds like one of the leads going into the CRT socket is broken loose from the lug. Have you checked there? Or maybe one of the lugs is not making contact with the CRT pin.

[ggregg]

My RA-109 had a similar issue. It was coming out of the doubler circuit. Cleaning eliminated the issue, for now anyway. It was up by the caps things that attach to the top of the tubes. Carbon traces, I assume.

[kramden66]

Yes virginia you are a doorknob .... it was the doorknob connecting the tops of the 1x2 tubes , i wasn't sure until i felt the doorknob and it was hot , so i swapped it with the one going to ground and the one at the caps of the 1x2 tubes remained cool , the one now connected to ground was getting hot , replaced the ground one with a ceramic disc cap rated at 15kv and then there was no arcing at all , the only issue that remains now is theres the anode wire where it connects to the pin on the 1x2 , it has a nice field around it , the wire has a couple threads that are loose and they stick up like moe's hair when he is scared , so i just have to insulate that area.

All agree its ok to leave the ceramic in ?

this motivates me , i may yet remove the crt to clean it and the glass

mike

[John Folsom]

That wire with the broken strands, better to replace it, or at least coat the brea of the broken strands with a smooth bead of solder. Any sharp points will create corona, and will likely continue to cause problems even if you attempt to insulate them

[kramden66]

theres a weird pattern on the side ( first picture ) that will pretty much go away when you fine tune (if you look closely you can still see it when tuned out but barely ) , here i made it as noticeable as possible in the picture so one can see the pattern and visable when screen is black , also you can see little ghosts/shadows on the letters , thats an if issue ? the ifs need to be realigned ?

its coming along atleast i've got a picture , the vert and horz are almost right without tinkering but for a better overall picture i will tweak them.

mike