Advice Admiral 12X12 20Z1 low contrast w/ lines - Page 3 - Videokarma.org TV - Video

Yamamaya42 · #31 01-21-2021, 06:23 PM

Quote:

Originally Posted by Kevin Kuehn

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.

vaporized metal from what?

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

Electronic M · #32 01-21-2021, 06:56 PM

Quote:

Originally Posted by Yamamaya42

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

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

Kevin Kuehn · #33 01-21-2021, 07:07 PM

Quote:

Originally Posted by Yamamaya42

vaporized metal from what?

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.

https://antiqueradios.com/forums/vie...hilit=ion+burn

Yamamaya42 · #34 01-21-2021, 07:28 PM

Quote:

Originally Posted by Kevin Kuehn

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.

https://antiqueradios.com/forums/vie...hilit=ion+burn

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

Kevin Kuehn · #35 01-21-2021, 08:46 PM

Quote:

Originally Posted by Yamamaya42

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

What, you didn't find that fascinating reading???

Yamamaya42 · #36 01-21-2021, 09:17 PM

Quote:

Originally Posted by Kevin Kuehn

What, you didn't find that fascinating reading???

I did not say that!

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..."

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

MadMan · #37 01-22-2021, 01:03 AM

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.

compucat · #38 01-22-2021, 09:47 AM

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.

Kevin Kuehn · #39 01-22-2021, 10:15 AM

Quote:

Originally Posted by compucat

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.

dieseljeep · #40 01-22-2021, 11:10 AM

Quote:

Originally Posted by Kevin Kuehn

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.

rca21d645 · #41 01-22-2021, 04:03 PM

Quote:

Originally Posted by Kevin Kuehn

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 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.

Tom9589 · #42 01-22-2021, 04:05 PM

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.

rca21d645 · #43 01-22-2021, 05:04 PM

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.

rca21d645 · #44 01-23-2021, 02:22 PM

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.

Kevin Kuehn · #45 01-23-2021, 03:45 PM

Quote:

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.