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  #31  
Old 09-19-2018, 09:40 PM
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So, I was messing around with the TV and letting it run for a little bit. Lost the vertical hold from a few resistors soaring in value. Fixed that, but still can't get a crisp picture from this set. I can adjust the focus magnet to get a pretty good image, but it sorta stops at a point. Any ideas?

Also, anyone know where I can obtain test picture tube? Brushing up against the CRT isn't my definition of fun. I haven't seen any round versions on the Bay recently.
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  #32  
Old 09-19-2018, 10:20 PM
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Do you have the brightness most of the way up? If so it could be that the CRT is near the end of it's useful life, which at that point the electron gun looses it's ability to focus well. It's also dependent on HV, so it could be that your HV is still on the low side. Try dimming the room lights and see if bringing the brightness down helps sharpen the picture any.

Another thought is if the ion trap is on the neck reversed end for end it could be limiting your overall brightness.

Considering the amount of ambient lighting in your shop I'd suggest your CRT is doing it's level best at producing a decent picture. These early tubes were never intended to be watched in a well lit room. The screens simply can't produce a high enough level of contrast with the brightness turned up high. Just remember that the CRT face can only go as dark as the ambient light reflecting off it's face. In other words the CRT can't make it self go any darker, it can only lighten up. That's ultimately what limits your contrast. Hope that makes sense.


Last edited by Kevin Kuehn; 09-19-2018 at 10:42 PM.
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  #33  
Old 09-19-2018, 10:52 PM
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One of the 8" rectangular test tubes with the same base (8AXP4 IIRC) will work on the early sets, but the screen will not be filled due to the difference in deflection angle.
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  #34  
Old 09-19-2018, 11:59 PM
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Quote:
Originally Posted by Kevin Kuehn View Post
Do you have the brightness most of the way up? If so it could be that the CRT is near the end of it's useful life, which at that point the electron gun looses it's ability to focus well. It's also dependent on HV, so it could be that your HV is still on the low side. Try dimming the room lights and see if bringing the brightness down helps sharpen the picture any.

Another thought is if the ion trap is on the neck reversed end for end it could be limiting your overall brightness.

Considering the amount of ambient lighting in your shop I'd suggest your CRT is doing it's level best at producing a decent picture. These early tubes were never intended to be watched in a well lit room. The screens simply can't produce a high enough level of contrast with the brightness turned up high. Just remember that the CRT face can only go as dark as the ambient light reflecting off it's face. In other words the CRT can't make it self go any darker, it can only lighten up. That's ultimately what limits your contrast. Hope that makes sense.

When I do most of the adjustments, I keep the lights down, Iíve found that the fluorescent lights are way too bright, but that a light on in the back isnít too bad. Brightness isn't bad, I have it up at about 3/4 brightness. Any more and the image washes out. The HV is still running lower than spec. (still 7.5kv) I replaced a bunch of resistors in the both the horizontal and vertical sections to fix a few issues. Iím gonna try injecting a composite signal tomorrow to see where that gets it. Hopefully itíll make it easier to make adjustments that way. Also, is there an easy way to tell which way the ion trap goes? I donít think the one on the unit is stock, and it doesnít have an indicator.

Quote:
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One of the 8" rectangular test tubes with the same base (8AXP4 IIRC) will work on the early sets, but the screen will not be filled due to the difference in deflection angle.
Ok, great to know. Murphyís law, thereís none listed right now. Iíll keep a look out
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  #35  
Old 09-20-2018, 12:05 AM
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Quote:
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I can adjust the focus magnet to get a pretty good image, but it sorta stops at a point. Any ideas?
.
When you say adjust the focus magnet are you adjusting the focus magnet itself or the focus potentiometer?
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  #36  
Old 09-20-2018, 06:41 AM
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When you say adjust the focus magnet are you adjusting the focus magnet itself or the focus potentiometer?
Focus magnet, to my knowledge the H22 series only has mechanical focus.
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  #37  
Old 09-20-2018, 10:29 AM
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Two things that may be worth doing towards the end of fixing the low HV: 1.) If you haven't done this yet and have several good 1B3s try swapping different ones in (tube testers while good at IDing dead HV rects are a poor indicator of how good they will do in a set). 2.) If a tube rect does not help try an SS HV rect...They made SS plug-in R-3A3s that will work in place of a 1B3, or if that is hard to get 5KV (or higher) PIV rated diodes are inexpensive online I'd grab 3-4 5KV diodes, string them in series and install them in place of the tube...Elimination of the HV rect tube filament load from the fly by switching to SS rect may bring the HV to spec.
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  #38  
Old 09-20-2018, 12:16 PM
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Elimination of the HV rect tube filament load from the fly by switching to SS rect may bring the HV to spec.
And don't forget there was some discrepancy between Riders and SAM's as to what the HV rectifiers series filament dropping resistor was suppose to be in this set. An ohm or two can make a big difference when it comes to a low voltage heater.
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  #39  
Old 09-20-2018, 07:00 PM
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Alright, so I substituted a brand new (5 in carton) 1X2B in for the HV rect. and I'm still having issues. The HV is still low, I'll probably try replacing it with the 1.2 ohm, though the one currently in the set is a 3.3 ohm. If that doesn't work, I'll try the solid state idea.
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  #40  
Old 09-20-2018, 07:45 PM
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For a quick test you can tack a second 3.3 ohm in parallel. That way you'll save all the work of removing the original in the event that it makes no difference. However there's also the concern of keeping the solder joins round and smooth in that high voltage area. Sharp points are more prone to arcing.
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  #41  
Old 09-22-2018, 01:23 PM
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Well, I was able to get a pretty decent picture and did my best to adjust it. Is the ion trap supposed to be so close to the focus magnet? The only way I can get a picture is either pushing it right next to the focus coil or almost to the end of the neck. I thought it was supposed to be midway on the tube.

I had to order the resistors because I didn't have any that low.
Thanks for everyone's help so far,
Zach
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  #42  
Old 09-22-2018, 04:20 PM
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The trap position varies from tube to tube. One trick is to take the trap off and flip it around such that the opening that faces the socket instead faces the screen.

Common position is close to the socket, but I have seen them mounted all over the neck.
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  #43  
Old 09-25-2018, 07:53 PM
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I suppose it's possible someone replace the ion trap with the wrong type. There are double and single magnet types. I would guess any 12" CRT from that time would use the double magnet? It usually specifies in the CRT type specs.
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  #44  
Old 09-26-2018, 10:38 AM
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Quote:
Originally Posted by Kevin Kuehn View Post
I suppose it's possible someone replace the ion trap with the wrong type. There are double and single magnet types. I would guess any 12" CRT from that time would use the double magnet? It usually specifies in the CRT type specs.
Iíll have to try it, the screen does have a little burn in in on the front of the tube from prior usage. The data sheets mentioned a single field ion trap, Iím assuming that means a single magnet ion trap.

Interestingly, the one shown in the service manual is different than the one that was on the tube.
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  #45  
Old 09-26-2018, 04:39 PM
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The data sheets mentioned a single field ion trap, I’m assuming that means a single magnet ion trap.

Actually there's quite a few with a single magnet on the side that have two sets of bars extending to clamp around the neck. If I'm not mistaken those would qualify as a double field. I'll see if I can find textbook examples of the two types. Can you see the type number on the neck of the CRT in your TV?

Last edited by Kevin Kuehn; 09-26-2018 at 04:47 PM.
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