Advice Admiral 12X12 20Z1 low contrast w/ lines

[rca21d645]

Originally Posted by Kevin Kuehn

Huh. What are the specs on that cap, I can't make them out in your picture. All too often I assume people have all the old caps and out of tolerance resistors replaced.

0.5uF 200V, just like the old paper one that was there before it. I've also been very weary about bulk replacements of parts, as it didn't go well with my RCA Victor console TV.

[Kevin Kuehn]

Originally Posted by rca21d645

0.5uF 200V, just like the old paper one that was there before it.

If that's the .5uf that returns the bottom end of the horizontal yoke winding to B+ I'd put something in there rated for high ripple current and more like 600-1000 volts. Ideally a physically large cap that can dissipate some heat. That little mini box cap didn't stand a chance with the high AC current flowing in that circuit.

[rca21d645]

Originally Posted by Kevin Kuehn

If that's the .5uf that returns the bottom end of the horizontal yoke winding to B+ I'd put something in there rated for high ripple current and more like 600-1000 volts. Ideally a physically large cap that can dissipate some heat. That little mini box cap didn't stand a chance with the high AC current flowing in that circuit.

I'll see about getting one rated for a higher voltage, the capacitor was about an inch wide and I don't know if you can even get ceramic capacitors much bigger than that.

[rca21d645]

I've been doing a bit more testing and just noticed something even stranger, the brightness knob seems to be working backwards now, the higher I turn it the darker the picture gets. I've also noticed the tube have brief flashes where it goes bright then turns off, I think this might mean the picture tube is internally shorting, but I'm not sure. It usually goes back to normal if I lightly wack the side of the tube.

[Notimetolooz]

Originally Posted by rca21d645

I'll see about getting one rated for a higher voltage, the capacitor was about an inch wide and I don't know if you can even get ceramic capacitors much bigger than that.

Why are you looking for a ceramic cap to replace a paper? A film would be the usual choice.

[dieseljeep]

Originally Posted by Notimetolooz

Why are you looking for a ceramic cap to replace a paper? A film would be the usual choice.

I have to look at the junk chassis, I have and see what's used in there.
The Sams photo shows a rather large capacitor for a unit rated at 200 volts.
I bet the original cap was an oil capacitor like some of the old coupling caps used in the electrostatic sets.

[rca21d645]

Originally Posted by Notimetolooz

Why are you looking for a ceramic cap to replace a paper? A film would be the usual choice.

I miss spoke, I did find a film capacitor to replace it.

[Kevin Kuehn]

.5uf @ 200v was a physically big cap back in 1948-49. My 20Z1 parts chassis has a Cornell Dubilier Grey Tiger in that posisiton, nothing special do you think? Rule of thumb - if it's overheating you need more surface area = higher voltage modern cap

[rca21d645]

Originally Posted by Kevin Kuehn

.5uf @ 200v was a physically big cap back in 1948-49. My 20Z1 parts chassis has a Cornell Dubilier Grey Tiger in that posisiton, nothing special do you think? Rule of thumb - if it's overheating you need more surface area = higher voltage modern cap

I replaced the burnt out one with a .47uF at 400v film capacitor and it seems to be doing fine. I also figured out the brightness knob making the picture darker was due to the ion trap moving slightly between me moving the television upright and on its side. The picture doesn't actually look half bad now in darkness.

[Kevin Kuehn]

Originally Posted by rca21d645

I also figured out the brightness knob making the picture darker was due to the ion trap moving slightly between me moving the television upright and on its side. The picture doesn't actually look half bad now in darkness.

Ahh making more headway. Now if you only had a way to measure the high voltage we could cross that one off the list. Any chance there are any TV repair shops in your area that are still open? Sometimes they have such items as a high voltage probe laying around and no longer using. That's actually a very linear image you have set up there.

[Electronic M]

Do you have video on the screen to tell if the raster is expanding when the brightness drops as you increase the brightness knob? If the raster is expanding (blooming is the correct term) then that means the brightness control is working but as the beam current increases with brightness setting the HV is loading down and sagging. If the HV is sagging your HV rect would be the likely cause but other horizontal issues are possible.

[rca21d645]

Originally Posted by Electronic M

Do you have video on the screen to tell if the raster is expanding when the brightness drops as you increase the brightness knob? If the raster is expanding (blooming is the correct term) then that means the brightness control is working but as the beam current increases with brightness setting the HV is loading down and sagging. If the HV is sagging your HV rect would be the likely cause but other horizontal issues are possible.

I haven't taken video of that, but the raster does expand a bit when I turn the brightness knob

[rca21d645]

Originally Posted by Kevin Kuehn

Ahh making more headway. Now if you only had a way to measure the high voltage we could cross that one off the list. Any chance there are any TV repair shops in your area that are still open? Sometimes they have such items as a high voltage probe laying around and no longer using. That's actually a very linear image you have set up there.

There actually used to be one about 5 minutes away from me, but sadly it closed down 4-5 years ago because the man running the place had become too ill/old to stay open.

[dieseljeep]

Originally Posted by Kevin Kuehn

.5uf @ 200v was a physically big cap back in 1948-49. My 20Z1 parts chassis has a Cornell Dubilier Grey Tiger in that posisiton, nothing special do you think? Rule of thumb - if it's overheating you need more surface area = higher voltage modern cap

I still maintain that it's an oil cap.
Consider the Zenith safety cap used in the 25FC58 or so. The original American Radionic cap. When I replaced them, I would take the hammer to them to see what caused them to fail. There was a oily film to the inside.
I never smashed the orange Spragues, as the were always good.

[Kevin Kuehn]

I tried to find some specs on the CD Grey Tiger series but I came up empty handed, other than electric guitar player's seem to think the ones originally used in their guitars tone control were the holy grail of sound goodness.