Advice Admiral 12X12 20Z1 low contrast w/ lines
 

After replacing the vertical output transformer and most of the capacitors, I was able to get a very dim, but visible picture by turning the contrast and the brightness all the way up. I noticed that no matter what I adjusted these lines stayed on the picture. I'm guessing this means there's an issue with either the brightness or the contrast, but I'm not certain. The lines look a lot like the retrace lines that appear when you turn up the brightness too high on older B/W computer monitors, but these lines don't disappear no matter how low the brightness is turned. Audio still comes in just fine.

here's a better picture of what it looks like, it shows up better in the dark. I also attached a link to a video of the television here: https://drive.google.com/file/d/1209...ew?usp=sharing

Looks like a tired CRT or low HV. Are you able to measure the HV ? Should be around 9 kV.

I don't think I have any easy way of measuring the high voltage as I don't have a high voltage probe, however I do know that the picture tube is fairly worn out but I didn't think that that would cause the retrace lines to appear like that.

Turning up the brightness and contrast on a weak CRT causes the retrace lines to appear.

Also the image has that ghostly almost inverted appearance common with weak CRTs.

There is a retrace suppression modification that can easily be added.

You can find it in Vol 1 here: https://www.earlytelevision.org/rider_cures.html

The download isn't working and I think the site hosting it is down, is there any other way to find this guide? Also would a weak tube have retrace lines appear when the brightness and contrast are turned all the way down? Because no matter which way I adjust the brightness and contrast the retrace lines stay on the screen, even if I turn them to the point of no longer seeing a picture.
Edit: I found it using the Wayback Machine

I also just noticed that turning the brightness all the way down made the picture clearer but the retrace lines remained on the picture.

Does your focus control seem to have any influence on the picture sharpness, as in can you make the scan lines more or less defined? Also can you make the CRT go all the way dark using the brightness control? When I say dark I mean can the brightness make the CRT go as dark as when the set is turned off? From what you said earlier about the retrace lines never going away it sounded like the the brightness would not cut off the picture.

I don't have a schematic, but there should be about 3 (maybe 4) peaking coils closely adjacent to the video output stage. Have you checked those for continuity?

Here you can download both Sams and Riders from the ETF

https://www.earlytelevision.org/tv_s...s_admiral.html

its most likely you just have a very weak CRT,,, have you tested it yet?

Turning the brightness down does not make the tube completely dark, and the focus control does effect the sharpness.

I have not, but I'll check them tomorrow and let you know.

The CRT did test fairly weak, but like I said I don't think a weak tube would make the retrace lines unable to go away.

Well what kind of DC voltage range do you read from the wiper leg of the brightness pot when you rotate it from one end to the other? One would expect approximately 150v at one extreme and 0v at the other. Referenced from chassis ground.

Was the weakness emission, cutoff or both?

I have the same CRT in my FADA, but it's hooked in differently, the cathode on mine is grounded, and video fed into G1.

The voltage readings for each pin on yours is listed on the SAMS, also you need to be sure you have a good video to the cathode, not sure what it will be for yours, but mine was about 39v PtP, my guess yours should be about the same, but inverted, since its going to the cathode, as opposed G1 on mine.

You also need to find a way to check that you have good HV, if it is low, it may be causing you problems, and/or a misaligned / weak ion trap.

But however, if all checks nominal, you most likely have a very tired / dead CRT, and must find another, and most likely end up paying way too much to some fool on Ebay, like.

https://www.ebay.com/itm/Vintage-Syl...-/174589841825

I just checked this morning, it goes from 0V to about 165V.

It had weak emissions but the cutoff seemed fine

Also after doing the modification to remove the retrace lines it did make them dimmer but they're still there even at the lowest brightness setting.

Is the 12LP4A a common tube, would it be possible to find someone willing to sell one on here?

All you can do is ask in the classified area, and hope, and you do not have to limit yourself to a 12LP4A exactly, if you find a 12LP4, ( same CRT, but without the gray face ) you could use that, or some other compatible one, for example a 12KP4 will work, just leave off the ion trap, I'm sure there are others that can work as well.

Also, when I was bringing up my FADA, I did not want to risk hurting my 12LP4, so I used a 8YP4 Test CRT that I got from ETM, not exactly the right one to use, but it worked for me with some minor mods! :)

you can see it all here :p
http://videokarma.org/showthread.php?t=272325

Thanks for the advice, I'll try the classifieds.

Here's what it looks like with the retrace supression modification. The lines aren't really visible so long as the brightness is turned all the way down, however if I turn the brightness up at all they appear. I also noticed that the longer I leave the set on, the more visible the lines become. I'm guessing this might be an issue with the high voltage?

from another source...

"A CRT with weak emission can produce a picture that's dim overall, and if you crank up the contrast and brightness in an attempt to improve it, the picture can get a silvery or almost-photo-negative appearance. Kind of hard to describe, but easy to recognize if you have seen it before."

This very much describes what was seen on yours, where it's hard to tell if you have good HV just by looking at yours, there does not appear to be any blooming, a good sign of it being low, but the only real way to be sure is to use a HV probe.

ETF has a sub guide.
https://www.earlytelevision.org/pdf/...guide_1959.pdf
any in the group 7 if I remember, can be used.

I'm pretty sure it is a very weak CRT. I'm not sure why the brightness control can't cut the picture off completely. Just for kicks I fired my 12X12 chassis up with a known very low emissions 12KP4 and get the same weak silvery appearing picture, although I do have complete control over the brightness all the way to dark. Measuring the DC bias at the video output could possibly shed more light on that issue. Half the fun of this hobby is figuring out why things are doing what they do. :thmbsp:

I see some neck shadow on the screen, that would indicate some mis-adjustment of the Yoke, Focus coil or Ion trap. The Ion Trap in particular can cause a dim picture.

Ion trap is for sure very sensitive. And if you don't get it right you risk depositing vaporized metal on the back side of the phosphor, which eventually leads to an area that shields the phosphor so it can't light up properly. Many folks mistake it for Ion burn, but it is not Ion burn because it's only visible when the CRT is operational.

I checked the horizontal output tube and the HV tube and both measured bad on emissions. I was able to swap the 6BG6 with another that tested ok, but I don't currently have another 1X2 tube to swap for the HV. I also changed a resistor on the HV which measured as 446k in the spot where a 1 meg resistor should be, so I put in a 1.1 meg resistor that I had on hand. The picture looks significantly better but now the audio is worse, with a fairly loud hum drowning out the audio, much more than it did originally. Video of it working here: https://drive.google.com/file/d/1rF1...ew?usp=sharing Photos are with the brightness turned all the way down.

I tried adjusting the ion trap after reading this, as well as the focus coil and I think I got the picture as good as I can.

vaporized metal from what? :scratch2::yikes:
https://i.imgur.com/1lkZjXx.jpg

quick look at mine....

https://i.imgur.com/ydVQqjS.jpg
https://i.imgur.com/hXdGhq1.jpg

setup looks like it does in the diagram :yes: :D

If a CRT checks good then around $100-150 is a fair price for it.

Vaporized anode aperture material being re-deposited onto the back surface of the phosphor.

Go to pages 62 and 84 of this pdf. http://www.americanradiohistory.com/...cs-1955-04.pdf

Tim over on ARF posted that above link in this thread, which was the first time a lot of us seen the light. :D
https://antiqueradios.com/forums/vie...hilit=ion+burn

mine looks correct, that is all I need to worry about! :banana:

What, you didn't find that fascinating reading??? :boring: ;)

I did not say that! :nono:

there was a bunch of old almost forgotten info in there.


I just got a bit nervous when you said " you risk depositing vaporized metal..." :scratch2:

and I had to make sure mine was correct, %100 :D

My Admiral set should be very similar. My focus potentiometer was open, and melted inside. Couldn't turn it all the way around. Caused some weird issues like this. Also, my ion trap was on backwards when I got it, and understandably, it kind of likes it better like that. I would desolder the focus pot and make certain it's not open. Also, try the ion trap backwards. My set has some neck shadow on the right lower corner naturally when the ion trap is at its best position, wouldn't worry about that.

Retrace lines were also a big problem, but largely went away with the retrace suppression hack. Tube is a little tired, only, but running on full brightness there are usually no retrace lines, unless maybe a particularly dark scene.

And also, if you're sure everything else is sorted, try the DC restoration hack Dobulee helped me come up with. It also helped a tiny bit with retrace, as I recall. It's not perfect, but it takes the edge off of suddenly light / dark scene transitions. Here: http://videokarma.org/showthread.php?t=269533&page=6
Use the latest schematic for that. Also there's a schematic for the retrace blanking I used as well, in case it was different.

Definitely looks like a heater to cathode short in the CRT. Such a short causes retrace lines and renders the brightness control ineffective. It happened once on my Motorola 9VT1 on the 8BP4 CRT and I blasted the short with my CRT tester and it was fine afterward.

That very well could be the case. But a heater to cathode short should show up on the tester, provided the OP checked for shorts.

I sold him the power transformer for that set! Little did I know he would have that much grief with the set.
Then Alexander PMed me that it needed a vert output transformer for it. No luck. He got one from someone else and now the CRT issue.
I haven't worked on one of those sets for at least 60 years. The set was a lot newer then and less to go wrong.
BTW, one of the first things I invested in was a 8XP4 test CRT. Subbing the questionable CRT with test tube, proves that the CRT is really the problem or not.
Dave. :boring: