Advice Admiral 12X12 20Z1 low contrast w/ lines

[Kevin Kuehn]

Originally Posted by rca21d645

After checking all the resistors I noticed that quite a few of them had drifted in value significantly, and have ordered some replacements, also here's a photo of that capacitor that fried.

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.

[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