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 Post subject: Admiral 24A12 picture
PostPosted: Dec Mon 08, 2008 7:48 pm 
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A couple screen shots below of my Admiral 24A12. I had a hard time getting decent pictures, won't show up good unless I turn the lights out, looks much sharper in person. I did a re-cap and alignment on this set about 12 years ago. Where that 12 years went I'll never know :shock: I just fired it up again for the first time since back then this last weekend. I was pleasantly surprised when it came back to life.

I have a question for you TV experts. In the first picture you can see pretty clearly a cross-hatch in the picture. I don’t really understand what’s causing this or if its normal. Seems to be its worst with the picture tuned and focused-in at its sharpest. This is with a cable feed. I was wondering if its possibly from a very strong signal? Would appreciate any comments and if its correctable where to go looking. Its not really noticable when you back up a few feet, so maybe its best to leave well enough alone?

Image
http://www.chibardun.net/~kjkuen/Admiral2.jpg
http://www.chibardun.net/~kjkuen/Admiral3.jpg
http://www.chibardun.net/~kjkuen/Admiral4.jpg

Kevin


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 Post subject:
PostPosted: Dec Mon 08, 2008 8:29 pm 
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It's either Sgt. Pepper interference or a too-strong cable feed.

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 Post subject:
PostPosted: Dec Mon 08, 2008 8:33 pm 
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Looks to me like AGC leakage into video signal. Might check video detector diode.
Also, I see what looks like slight picture fold over.. Vertical output problems??
Bill Cahill

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 Post subject:
PostPosted: Dec Mon 08, 2008 8:44 pm 
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Don't worry about the foldover, unless you see it in real life. Most likely a camera exposure time issue (catches one or more frames plus one fractional frame - very common problem when photographing a TV screen).

Some additional thoughts on the cross-hatch:

- Can be interference coming from the cable box (if used). Sometimes these emit some interference that an old TV picks up through its internal twin lead antenna wiring (modern TVs are less sensitive to this problem). Try moving cable box physically farther away from TV.

- Can be chroma signals. Usually these are pretty fine scale, and yours looks a little too coarse. But I thought I'd mention it. Chroma signal interference is normal in old B/W TVs, and not really very objectionable. In fact, if you can see it, your alignment and focus are very good, so you should be mostly happy.

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 Post subject:
PostPosted: Dec Mon 08, 2008 8:55 pm 
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Tom Albrecht wrote:

- Can be chroma signals. Usually these are pretty fine scale, and yours looks a little too coarse. But I thought I'd mention it. Chroma signal interference is normal in old B/W TVs, and not really very objectionable. In fact, if you can see it, your alignment and focus are very good, so you should be mostly happy.


No cable box involved. No vertical foldover in person, its the camera effect. Must be the chroma signal, I remember aligning this thing to death back then :lol: Again, it looks magnified in the picture, my camera does not like moving pictures in the dark, its more subtle watching the TV. Glad to hear its nothing alarming. I'm happy.

[edit] if I de-tune the picture a little, it pretty much is gone. Of course the audio is not so great then.

Thanks for the suggestions guys, keep em coming if you have another idea.

Kevin


Last edited by Kevin Kuehn on Dec Mon 08, 2008 10:29 pm, edited 2 times in total.

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 Post subject:
PostPosted: Dec Mon 08, 2008 10:15 pm 
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It just occurred to me…I resoldered that 300-ohm antenna lead(at the back antenna connection) going to the tuner. It originally looped up and over the chassis. Could that being too close to the chasses cause the crosshatch? I have the power supply chassis apart right now for a little clean up, I’ll try moving the antenna wire later.

By the way, the high voltage cage cover was missing from my set when I got it, any chance of finding something like that? Should be easy enough to make one. I can’t imagine why any service person would have left that off?
Image

Kevin


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 Post subject:
PostPosted: Dec Mon 08, 2008 10:56 pm 
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I'm not prommissing it, but, that could be adding to it. I have found that all Admrals have antenna lead dressed from the chassis. I'd re dress it. Simple enough.....
If that doesn't work, tune for best picture, and, adjust audio Deteector transformer for best sound, with least hum.
If that fails, try re aligning the audio IF stage.
Bill Cahill

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 Post subject:
PostPosted: Dec Wed 10, 2008 4:51 pm 
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I’ve been watching this Admiral TV on Ebay and noticed that besides the HV cage cover, my set is missing the metal bracket at the lower back of the upper chassis. Its the thing right below the bottom rear edge of the top chassis. Looks like it screws into the Bakelite case on both sides of the uper support shelf. Anyone know what the purpose of that bracket is, possibly an antenna mount? I don't recall ever having it, or else I've misplaced it or thrown it out by accident. This sort of thing that happens when I drag a project out to long :oops:



Image

Kevin


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 Post subject:
PostPosted: Dec Wed 10, 2008 7:02 pm 
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Hi Kevin,
That bracket your missing is what the original back would have attached to. The back was molded in such a way that it formed a box shape instead of being flat. Since the center of the back was higher than the edges, the bracket was used to keep the center of the back tight.
-Tony


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 Post subject:
PostPosted: Dec Thu 11, 2008 7:32 pm 
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Tony V wrote:
Hi Kevin,
That bracket your missing is what the original back would have attached to. The back was molded in such a way that it formed a box shape instead of being flat. Since the center of the back was higher than the edges, the bracket was used to keep the center of the back tight.
-Tony


Ah...that makes sense now. Also allowed cords to go between chassis I suppose.

I guess since I don't have a back I don't need it. :D

Kevin


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 Post subject:
PostPosted: Dec Thu 11, 2008 7:36 pm 
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Ok, back to my original question...I tried moving that 300 ohm antenna lead around and I can’t see any effect on the cross hatch. I do think I’ve verified that it’s the chroma information causing it. I really don't have a good understanding of of how the chroma signal works.

Here is a screen shot of the B & K 1077B with the color off.

Image

Here it is with the color turned on, honeycomb or crosshatch shows up.

Image

Does this make sense? Is there any way of filtering this out? I wonder if any VCR’s, DVD players, or cable boxes have a B&W/ color switch on them?

Kevin


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 Post subject:
PostPosted: Dec Mon 15, 2008 7:47 pm 
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I have a TV dummy question. :) As some of you may have noticed, my test image picture above seems to have a slight arch in the scan lines(more-so towards the top).

IMO the linearity is pretty good(a little short at the bottom), adjusting vertical linearity does nothing for the bend at the top of the screen.

Any idea's what would be causing this condition? I notice my focus coil is tilted in at the top and out on the bottom quite a bit. I can't remember exactly why I have it this way, but it seems it was the only way to get the picture centered at the time.

Would appreciate any advice.

Kevin


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 Post subject:
PostPosted: Dec Mon 15, 2008 10:50 pm 
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Here’s a picture of the angle my focus coil is set at. Always seemed a bit excessive, yet that’s where the picture centers on the screen :?
Image

Kevin


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 Post subject:
PostPosted: Dec Tue 16, 2008 12:42 am 
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Hello Kevin Kuehn,
well far as your back cover goes is it just a flat coverf or is it baklite or just metal it could be support for the back cover .It also could be where a couple powercord hangers go or as you said antenna mount do you have a back or not with yours .
sincerely Rich


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 Post subject:
PostPosted: Dec Tue 16, 2008 12:46 am 
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radiorich wrote:
Hello Kevin Kuehn,
well far as your back cover goes is it just a flat coverf or is it baklite or just metal it could be support for the back cover .It also could be where a couple powercord hangers go or as you said antenna mount do you have a back or not with yours .
sincerely Rich


My TV doesn't have a back. I've read they are a very rare find with a back still in place.

Kevin


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 Post subject:
PostPosted: Dec Tue 16, 2008 12:48 am 
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Hi Kevin,

Chroma interference is common in sets that old. Many of them are capable of delivering a sharper picture than would have been available after color came along. This is due to the IF bandwidth. You could misalign the IF to deliberately make it like a late 50's set. I wouldn't.

For a quick and dirty fix, use a good VCR for the tuner. Pick one with a good comb filter. Comb filters vary in quality, a lot. All introduce other artifacts, but some a lot less than others. Theres gobs of information about comb filters online. Any of them will recover more high frequency information than is possible with simple LC circuits.

Take the s-video output from that VCR and make a custom cable that connects to only the luminance/sync channel. Plug that (and the sound) into the composite video (and sound) inputs of an RF modulator, or another VCR. Now you have true black and white with all the high-frequency video information the comb filter could recover.


John

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 Post subject:
PostPosted: Dec Tue 16, 2008 5:10 am 
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blue_lateral wrote:
For a quick and dirty fix, use a good VCR for the tuner. Pick one with a good comb filter. Comb filters vary in quality, a lot. All introduce other artifacts, but some a lot less than others. Theres gobs of information about comb filters online. Any of them will recover more high frequency information than is possible with simple LC circuits.

Take the s-video output from that VCR and make a custom cable that connects to only the luminance/sync channel. Plug that (and the sound) into the composite video (and sound) inputs of an RF modulator, or another VCR. Now you have true black and white with all the high-frequency video information the comb filter could recover.


John

John,

Thanks for the great idea, why can't I think of this stuff :)

Looks like all a guy would need is one of these rf modulators
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0343729837

Then disconnect pin 4 (C) wire from the S video jack inside the box and use a regular S video cable too connect to the VCR.

Kevin


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 Post subject:
PostPosted: Dec Tue 16, 2008 5:16 am 
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You can get RF Modulators at Radio Shack, Target and Walmart. Cost about $19.99 each. I have one from Target that I use to play DVDs through my B/W Westinghouse TV...

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 Post subject:
PostPosted: Dec Tue 16, 2008 5:18 am 
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Don Cavey wrote:
You can get RF Modulators at Radio Shack, Target and Walmart. Cost about $19.99 each. I have one from Target that I use to play DVDs through my B/W Westinghouse TV...


Don, does your's have the S video jack?

Kevin


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 Post subject:
PostPosted: Dec Tue 16, 2008 5:50 am 
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It looks to me like that would work fine, or if you don't have an svideo input on the modulator, just jack it into the composite video jack...... or use a second VCR...... or......

Just as a side note, I have been told that to get rid of the pattern it is enough to notch out the colorburst (without removing the actual color modulation information from the signal). I have a little circuit board kit from Germany that is supposed to do exactly that (among other things). I haven't built it yet.

The svideo trick sounds better to me :)

John


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