Zenith 2250R

[Zsuttle]

Originally Posted by Electronic M

7.5KV should be enough to get some kind of light on a healthy 12" CRT...Try pulling the Vert output tube and see if you can get a horizontal line on screen. Is the ion trap of the CRT adjusted correctly, and do the electron gun bias voltages look reasonable?

One thing to be wary of is that if the horizontal oscillator is not running very close to the correct frequency the HV can become low (yet all the DC voltages on the output tube can be about right). If you haven't adjusted the horizontal osc with a scope and a frequency reference (the sync pulses on the composite video output of your signal source is a good reference), and you have never got video on the screen then the osc is likely to be off freq a ways.

That explains a few things, the horizontal oscillator was at 15.35khz instead of 15.75khz listed on the service manual. This might be a stupid question but what exactly gets adjusted? Do I adjust the master oscillator? Or is there an individual adjustment for the horizontal oscillator?

Sorry for all of the questions, still a newbie at this
~Zach

[Kevin Kuehn]

Originally Posted by Zsuttle

That explains a few things, the horizontal oscillator was at 15.35khz instead of 15.75khz listed on the service manual. This might be a stupid question but what exactly gets adjusted? Do I adjust the master oscillator? Or is there an individual adjustment for the horizontal oscillator?

Sorry for all of the questions, still a newbie at this
~Zach

The only horizontal frequency adjustment you have on this set is the horizontal hold control. Can you see the horizontal frequency change when you move that control to its extremes? I agree with Electronic M that you should see a raster even with 7.5kv. I'd try rotating the Ion trap around the neck and also forward and back in a dimly lite room, in hope that a hint of light shows up. Then the idea is to get it to the position where the screen is at it's brightest. Once you see any light, turn down the brightness and keep trying to bring it back with movement of the trap. Since you've had the CRT out there's no telling how far it's been moved from it's former working location.

[Zsuttle]

Alright, I guess it worked because I'm getting some sort of picture. It's not the greatest or clearest picture I've ever seen and actually, the voltage worked itself out. It's at around 9kv which is better than it was before. Here's a picture of it displaying the Indian head test pattern.
20180913_230010.jpg
20180913_231327.jpg
I'm still pretty new to the TV category, what else needs to be done to improve the image? I'll center it completely once I move it back into the cabinet, and looking back, I think the focus could be adjusted to be way better.

[Kevin Kuehn]

Originally Posted by Zsuttle

Alright, I guess it worked because I'm getting some sort of picture. It's not the greatest or clearest picture I've ever seen and actually, the voltage worked itself out. It's at around 9kv which is better than it was before. Here's a picture of it displaying the Indian head test pattern.
Attachment 197676
Attachment 197677
I'm still pretty new to the TV category, what else needs to be done to improve the image? I'll center it completely once I move it back into the cabinet, and looking back, I think the focus could be adjusted to be way better.

Good job!

Now try running though this horizontal setup procedure from your Sams folder 114-13 page 10. Hopefully you can get the pattern a little less egg shaped. Just remember these things were never perfect even back in the day when folks used them for their daily drivers.
Besides focus adjusting your fine tuning control may help clear up your image some too.

https://c2.staticflickr.com/2/1881/4...9748b076_b.jpg

[Zsuttle]

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.

[Kevin Kuehn]

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.

[Zsuttle]

Originally Posted by Kevin Kuehn

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, I’ve found that the fluorescent lights are way too bright, but that a light on in the back isn’t 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. I’m gonna try injecting a composite signal tomorrow to see where that gets it. Hopefully it’ll make it easier to make adjustments that way. Also, is there an easy way to tell which way the ion trap goes? I don’t think the one on the unit is stock, and it doesn’t have an indicator.

Originally Posted by Electronic M

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. Murphy’s law, there’s none listed right now. I’ll keep a look out

[Eric H]

Originally Posted by Zsuttle

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?

[Zsuttle]

Originally Posted by Eric H

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.