17LP4 CRT ( Need one... )
 

After removing my CRT and cleaning around the neck, I could clearly make out the crack you see in the photo I've attached to this thread. After closely examining photo's made prior to this, it appears that this crack was present all along and probably even before I brought the set home. The very dim picture along with this crack around the neck is enough to qualify this as a "bad" CRT, in my opinion. :thumbsdn:

If I am to bother trying to repair this set as intended, I will first have to find a suitable replacement 17LP4 ( or 17VP4) CRT. I'm not sure how many of these are around or what one will cost me, but if nothing turns up, I'm afraid this will force my Zenith into retirement as nothing more than an interesting piece of furniture. :tears:

If the phosphor, screen, hasn't been disturbed then Scotty should be able to rebuild it. Time is short though.

John

Short is right. Next week is it for Scotty :(

Next week? That would really be calling it close for me. Is this fellow retiring or something? How could I get ahold of him, assuming could get my CRT to him in time? I live in South Carolina, btw.

Yes, he's retiring. Here's an article about Hawkeye and here's the website.

Those are pretty impressive cracks. It's difficult to imagine that the tube hasn't gone up to air, but yet you say you still get a dim picture.

What does the getter flash look like? Is it still shiny?

Rebuilding is expensive and if you can get an NOS one, then if this one works well enough to keep you busy restoring the set, then I suppose it makes sense to use it until you find one.

John

Just my opinion on your tube...I'd agree about trying to find another one. Even if you shipped the one you have (cracked) the handling and shipping of something that is just more fragile may not make the trip.

If the "getter flash" is what I think it is, it's shiny. All of the visible parts of the beam gun look almost like chrome, aside from these 3 transparent cylinder things.

The light I could see coming from the neck of the tube when it was in operation was fairly decent, brighter than any of the other tubes. At night in a dark room, I could adjust the ion trap to get a full raster, bright enough to cast a glow a few feet from the tv. Turn on the lights, and it's practically nothing. I was able to get something of picture, at one point ( in the dark, of course ) although the images flipped and scrolled, and went slanted into chaos. Aside from this, I've also never gotten any sound other than a very small crackle from the speakers and I only heard this once or twice as the tv warmed up.

With the dim picture, I'd assumed that the CRT was bad all along but I didn't know about the crack until now. But, I also knew it needed caps and probably a couple tubes so it hasn't been turned on for months. Right now it's been taken apart ( there was no spark when I discharged the CRT ) and it's got a nice, clean chassis after I went through it last night and this morning.

I've already located a company that sells new 17LP4's, but it would cost $185. It would be oh, so very nice if I found one a bit more affordably than that. For now, I'll get my schematics, recap it, and test it with what I've got. I'll just pay attention to my CRT when it's running and see if it smells like ozone near the back...

If the company is Video Display Corp then most likely they don't have one, they list most every type but when you inquire they'll tell you it's a database error.

There was a NOS 17LP4 listed on eBay a while back for $25, don't know who, if anybody got it.

Yeah, VDC is the only one I found. If they didn't have it, then I guess it wouldn't be worth worrying about. It's expensive, anyways. I'll write them and find out, just to be sure. I saw the one for $25 and I think it sold. I ran across a thread about it here that was posted in the past year or two.

Just for grins, I have posted a picture of a CRT getter flash... It is an evaporated coating of barium deposited on the inside wall of the glass, to "pump" residual gas after the CRT is sealed. In this tube, the gun parts also look fairly shiny, but that is not what you are looking for... the getter flash is visible through a small rectangular window in the gray dag coating. It is shiny, and in this tube, exhibits some "rainbow" color around the edge.
Note: this tube uses cream colored ceramic supports for the gun elements, rather than the clear glass support rods seen in your CRT.
jr

Hmmm... in light of this information; is my getter flash still shiny? Eh... not so much...

What do you guys know about the interchangeability of CRT's? The one in my television was originally a 17LP4 and/or 17VP4. Are there any other compatible 17-inch CRT's that might interchange? If so, I'll have to keep a look-out for those also. So far, I've read about a couple different variations made during this period that are very similar to the 17LP4. The main difference I've noticed is that my CRT is uses an electrostatic focus, and many of the other types are magnetic. However, the 17RP4/17HP4 has nearly identical specifications to the 17LP4, and also uses an electrostatic focus.

Here's the specs for the 17LP4:
http://www.shinjo.info/frank/sheets/137/1/17LP4.pdf

Oh, and below is my not-so-shiny getter flash.

I have a 17lp4 that I do not need,it is stored in a plastic bin behind my garage.
Probably be able to get it out and test it this weekend
Pat

Look at your getter, it looks like it has been "got".

If you don't have a crt tester, there is an easy way to determine if the tube is very gassy. IT IS A DESTRUCTIVE TEST IF THE TUBE IS VERY GASSY!

1. measure the heater resistance... should be fairly low, like a few ohms.
2. apply 6.3 volts to the heater (Pins 1 & 12)... does it light up normal brightness? if so, the CRT may have a decent vacuum in spite of the crack and "used up" looking getter.
3. if it just barely lights up, it will likely burn out very quickly, perhaps you will see a flash. Tube is very gassy and now has a burned out heater.
4. re-measure the heater resistance... if the tube is very gassy, it is now likely "open".

Here is what happens...the heater resistance is much lower when it is cold than when it is hot. If the tube is gassy, air molecules will transfer heat away from the heater, so it will remain fairly cold. Since the heater resistance stays low, it will draw more current than it is rated for, and open up like a fuse.
Even if the tube is very gassy, continue to handle it carefully, as it still could have a partial vacuum, and be an implosion hazard.
jr

Hey, that tube might be just what I'm looking for! Let me know how it tests when you get around to it. If it's good, maybe we can work something out. @ grimer

Yeah, I don't think I have a way to apply voltage to my tube other than plugging it into my television. Or well... there is another possibility... but anyways, I read very little resistance across the heater pins, very low at first and then it fluctuated and came back to about 1 ohm or so. I guess I'll leave it be and see about getting the capacitors in order. Looks like I can get them all for about $40 from JustRadios.

Greetings from FixitLand!

The 17LP4 and 17VP4 have a cylindrical faceplate; that is, it curves from left to right (which you can see looking straight down its face) but vertically it is flat (which you can see looking across its face). (Sony Trinitrons were made the same way.) The 17HP4/17RP4 faceplate apparently curves both horizontally and vertically, as most tubes of that era do. So, electrically it may be quite similar, and actually work, but mechanically it will probably not fit the TV's picture mask properly.

My 1952 Zenith K1846R also uses a 17LP4 tube. So did my first set, a '53 Motorola TV-radio-phono unit.

Take care,
--
J. E. Knox 'The Victor Freak'

I had a 21fjp22 that did that, under the blue lateral magnet. Symptom was a dim picture. I cleaned off the neck, put some silicone around it. I turned the set on and left the house for ~4 hours, came back, fixed... pic was back to normal. No problem.

that's what I did to the cracked 10fp4-spread silicone over the cracks, and wrapped it tight in electrical tape. I could see how getting it sealed and running the filament would get the few air molecules moving enough to be gathered up by the getter-if there is any of it left.

Potentially you could have a perfectly good cathode still. The crack may have gotten onto your tube when someone carelessly bumped the back of the set against the wall, since the tip of the neck tends to stick out of the backs of many sets. Don't ask if this has happened to any of us!

Hm, I had been thinking to myself that maybe there was a way to seal the crack. But... I was under the impression that losing the vacuum ruins the tube and there was no way to get that vacuum back once air got in there.

So uh, I could seal my crack with silicone and run the set for awhile and see if that helps? Hm, since I don't have any way of running my filament other than the tv itself ( that I'm aware of ) I guess this is something I'll have to try once I get all my caps replaced.

You don't have anything to lose. However, silicone RTV is quite permeable to oxygen so it doesn't provide much of a seal.

http://www.silicones-science.com/grades_elastomers.html

John

Well, if luck is on this tube's side-would just putting something over the crack be of benefit? After all, the leak is rather small, so the perceived pressure gradient may not be too extreme. Are there any other relatively available materials out there that are relatively impermeable to the atmosphere but still effectively bond to glass?

If grimer has a good tube for you, that seems better all around than trying to seal a big crack.

There is an expensive product called Vacseal. Some folks apply it on the leak-prone parts of 15GP22 tubes on the theory that it can't hurt and might help prevent future leaks.

http://www.2spi.com/catalog/vac/vacleak.shtml

Even if you seal that crack, I'd be concerned that heating & cooling during normal operation could make the whole thing go PLINK at any time. Once a crack starts, the weakness may put stresses on the rest of the neck.

Phil Nelson

I used RTV-1. It worked fine for 2 years until the fly failed. The set was then pitched.

The Getter is white, this tube has gone to air, it's done.

The only thing now it to look for a replacement, they do pop up now and then you just have to keep looking.

Someone pointed out Epotek 353ND to me. It provides a nearly hermetic seal.

I'm inclined to agree with Eric.

It may have had a small crack to begin with, but under the stress of handling suddenly got much worse as Phil suggests.

I once tried to make a vacuum chamber by sealing pieces, that were assembled in the shape of a soccer ball, with RTV. We wanted to use a flexible material that wouldn't crack. We were unable to achieve a very good vacuum because of the permeability. We ended up overcoating the RTV with an epoxy.

John

BAd news,this tube I have here shows no sign of life at all,the filament lights up but no emission,even at 8 volts:thumbsdn:
But I suppose it was worth a try
Pat

http://i242.photobucket.com/albums/f...6/badcrt01.jpg

Is the heater lit?

Possibly re soldering the pins would help?

Yup,the filament lites up.I let the tube warm up for 20 minutes,even cranking
up the heater to 8 volts did not help.

I had the same problem with a 16KP4 recently - good filament, but 0 emmision. It turned out to be an open cathode. I was able to re-weld it by using the technqiue described over here: http://www.videokarma.org/showthread.php?t=248067
Just a thought.

Well, thanks for trying! If that tester can pull off that re-weld techique, it would be worth a try, but even then I know some tubes just are beyond repair.

Well guys, just keep the word out for me. Maybe I'll put out some WANTED posters... :smoke:

crt
 

I have a new zenith 17cqp4 in the box if you think it could work you can have it for the shipping.

That sounds great! It may take me a little research ( and some knowledgeable advice ) to figure out if this will work, though. I haven't found info on a 17CQP4 as of yet, but I've found specs on the 17QP4 which I suspect is closely related.

http://www.shinjo.info/frank/sheets/093/1/17QP4.pdf

Here's the good news! Physical specs are nearly identical! I believe the faceplate is the same shape and size, the neck is the same length, same overall length. Everywhere I see where it would matter, it should definitely fit my chassis and yoke. Electrically, the specs are almost identical to the 17LP4.

But, there are a couple of notable differences. There is one pin that the 17LP4 uses that is missing on this 17QP4, pin 6 (G4). It also states that this tube has magnetic focus instead of electrostatic focus. I honestly don't even know what that means, so I have no clue as to how interchangeable these two types are or what changes would need to be made to make one work in the other.

Does anyone have some specs on the 17CQP4 for comparison? I can't assume the 17QP4 is the same, and I don't know what the "C" in there indicates.

( double post ) I dunno how to delete it... lol

Magnetic focus uses an external magnet assembly, either electric or mechanical to focus the tube, electrostatic focus uses voltage to focus it internally inside the gun, that's probably what the missing pin is for.

You might get lucky and have it work without the magnet assembly but probably not.

But it might be possible to add a magnetic focus coil or permanent magnet assembly salvaged from another set to adjust focus on this tube. Years ago, I used an aftermarket add-on permanent magnet focus assembly called a Quam "focalizer" (or something close to that) to focus a crt in a set where the focus coil had failed... something like that might work.
jr

Right, I was thinking that. I wonder if this worked like it does on an electrostatic speaker where the magnetic field is created by current flowing through a coil, which would means the coil would have to be tapped into a circuit somewhere. Obviously, a permanent magnet would be much easier. I'll look into this a bit...

I'm still unsure about this type of tube and I wish I could find some specifics on it. I'd hate to pass up a NOS tube. In my opinion, changing to a magnetic focus would be an improvement over the electrostatic if it were possible. With the electrostatic type, I understand that the focus degrades over the life of the tube.

Here are a couple of pix of a permanent magnet focus assembly (mounted between the yoke and the ion trap) in my 1953 Philco... it would take a fair amount of mechanical modification to support such an assembly in your set, but it might be worth a try if you can't find the correct CRT. The focus adjust is the little brass knob on the flex shaft, shown on the second picture. The little lever, with the wing-nut lock at the top of the assembly is the position adjuster.
The Philco uses a 17YP4, which also has a cylindrical face.
jr

I have at least one spare PM focus assembly, if you needed it. I agree that it could be difficult to fit, depending on how the yoke is arranged.

I might have a spare assembly as well. It is a large ring magnet, so you don't need to make an electrical connection to it. It came out of a tv that I got a new crt for, and I had to change it from magnetic focus to electrostatic, which is much easier to do (just rip out the old m-focus hardware). If you need it, I'll see if I still have it.