I did check for shorts, and none came up. I've been using a Mercury 1000 tube tester as it is the only tube tester I own.

If you are concerned about a heater to cathode short, just get a separate filament transformer and wire it directly to the CRT after disconnecting the existing filament leads to the CRT. That will keep the cathode from being pulled down too low due to the heater to cathode short and restore the brightness control.

I also just noticed while checking resistors that the 0.5uF horizontal sweep coupling cap had partially melted itself, so that may also have been causing an issue.

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. :scratch2:

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.

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.

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.

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. :scratch2:

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

.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 :D

https://live.staticflickr.com/65535/...f4d91dcd_b.jpg

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.

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.:thmbsp:

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

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.

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.

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.:smoke:

Let's see here... crypt scribbling on the lower right corner, shedded pieces of wax from a dying cap, 3 paper cap (bombs), that are screaming to be replaced, :) , a soldering iron accident with the blue wire on the lower left corner, and what seems to be magnet wire very close to a metal chassis, :o

but, that's just a guess! :D

So I have the picture looking pretty good but the audio is now quieter and there's a loud hum drowning it out. I think it has to do with the vertical because turning the height and linearity controls makes the hum quieter.
Edit: upon further inspection it appears the audio output tube had gone bad between now and when I started this project, as the emmissions now test bad.

The voltage on the cathode of the audio output(pin 1) supplies 135v to the audio IF, tuner, video IF, and video out circuits. Basically the tube is used as a b+ dropper to supply the lower b+. If you operate the TV with the audio output tube pulled, those other circuits will loose their b+. Good to verify that 135v volts is in the ballpark.

I finally figured it out, one of the 6AL5 tubes wasn't making a good connection in its socket, and after moving it around a bit the audio comes in just fine.

That is why cleaning all tube pins and sockets is one of the FIRST things that I do in any restoration.

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

I had a problem with my Zenith 25MC33 color roundie where it looked like the horizontal AFC diodes had failed, classic symptom. I replaced them only to find the problem was a dirty socket for the horizontal oscillator tube.:stupid:

The new picture tube arrived today, and after installing it the picture looks great. I have full contrast and the brightness works fully with a nice sharp picture. It looks a bit dim in the photo because it was in a well lit room at the time.

Good deal. :banana: And that has got to be about the roundest test pattern one could expect , which means you have it adjusted perfectly.

I'm glad it worked out for you!
It was quite a hassle. First the power transformer, then the vertical output transformer and all the rest of the parts and work that was involved. :thmbsp: