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  #31  
Old 08-02-2014, 01:48 PM
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dtvmcdonald dtvmcdonald is offline
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The new resistor fixed the focus problem. I tried magentizing a
screw for a replacement purity magnet. It was not quite strong enough.
So I ground the top of the screw flat and superglued on
a small piece of a refrigerator magnet. This made it work OK.
Getting passable convergence was fairly easy.

I got around to playing with the B+adjustment resistors
I had installed. The B+ was at 355 and I got it up to 385,
which Sams says i Correct, so I left it there.

The only remaining problems are probably designed in ...
bright colors in large areas ruin the luma. Actually my Pilot TV-37
ha the exact same problem until I realigned it to not
overemphasize 3.58 MHz. The other problem
is serious blooming on white screens.

Pictures this evening when window reflections wont be
a problem. I'm not showing Dorothy ... my copy is pillerboxed.
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  #32  
Old 08-03-2014, 08:21 PM
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dtvmcdonald dtvmcdonald is offline
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Didn't take pictures last night. I decided that it still
was not right. Guess was that the drop in luma when full brightness
full saturation R appeared was caused by clipping in the detector
because the luma carrier was too far down on the 45 to 46.5
MHz slope, and the chroma was much much too high. I had looked
at the response crudely using a CH 10 rf sweep and it looked
like a sin curve from 46 to 41.25 MHz for the IF. I was unsure
of this since I didn't have a proper bias box.

Today I did an alignment. But there was a problem: the
cheapo Eico generator I got off Ebay leaked RF out the line cord.
That was fixed by removing the knot from the line cord,
shortening the leads to it, and installing new and better safety caps
as close as possible to the line in, the ground end soldered directly
to the chassis. The caps should be broadly series
resonant somewhere between 40 and 160 MHz. This worked.

Then I did the "Overall IF Alignment" on page 19 of the
RCA service manual. All the traps were already quite accurate so
I touched only 1T109, 1T110 and 1T111. This took a while with careful
notes of where I left everything since I wanted to be able to go back
if needed. 1T109 and 1T111 were within 160 degrees of
correct, but 1T110 had to go 1 1/3 turn clockwise. This resulted in
an almost perfect curve. The little bump
below 41.25 MHZ was a bit smaller than shown in Fig. 27.

I had earlier today generated true proper test patterns for an
IQ color set. I will make these available somewhere. They are
jpeg files generated in Photoshop by calculating Y, I, and Q levels
mathematically for various color patches.

The 2 main files have +I, -I, +Q, and -Q all at the same color level
and the luma calculated to make high saturation without going more than 5%
blacker than black or whiter than white. One file has full bandwidth
color (to 4MHz) in the jpeg, the other has I limited to 1.5 MHz and
Q to 0.5 MHz. (This was done by converting to Yab in Photoshop and
applying a "motion blur" to a and b only.) The -I to +Q transition was
filtered at 0.8 MHz.

I then copied the files to my Sony Blueray player and played them.

The result on the filtered IQ test are amazing. There are no off-color
fringes except a tiny one in -Q. The +-I transition is clearly three times
the resolution of the +-Q one. The unfiltered file shows
the expected 0.5 to 1.5 MHz crosstalk that so
mars cheapie color decoders (and encoders).

Its not as good as my 55 inch LCD TV on the same NTSC, but its close.

And the problem with saturated reds and yellows is gone.

Next is dinner.
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  #33  
Old 08-03-2014, 11:44 PM
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dtvmcdonald dtvmcdonald is offline
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Here are final result images. These are taken with a digital
camera and processed in Photoshop. I have not changed the color
but did brighten some. All were processed in Photoshop taking
care that no pixel was overloaded. The non-CRT dot images were
blurred correctly before resizing to avoid moire.

These are off-the air digital TV images.
The next post contains technical images.
Attached Images
File Type: jpg _MG_4447b.jpg (151.0 KB, 79 views)
File Type: jpg _MG_4447c.jpg (128.5 KB, 74 views)
File Type: jpg _MG_4454c.jpg (106.4 KB, 77 views)
File Type: jpg _MG_4455c.jpg (123.6 KB, 86 views)
File Type: jpg _MG_4468b.jpg (119.3 KB, 81 views)
File Type: jpg _MG_4476b.jpg (114.3 KB, 84 views)
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  #34  
Old 08-04-2014, 12:01 AM
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dtvmcdonald dtvmcdonald is offline
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The first one is the IF response. The marker is at the video carrier.

The rest are of the picture I made and played on my Blueray player
that contains images of R G B fully saturated but
different brightness on the top row, and +I -I +Q -Q on
the bottom row. The transitions on the top row were not
filtered in Photoshop (before playing the test file ... not the
camera images), while the bottom row was filtered to the
NTSC specs for the +_ I and Q transitions, and
filtered at about 0.8 MHZ for the -I to +Q one.

The final image is the histograms made from my
digital camera images of the flat (appropriately blurred)
parts of the patches. Its not perfect, and I also note that
I don't know what the gamma of the camera is ... this is
not photometric.
Attached Images
File Type: jpg _MG_4445.jpg (91.4 KB, 30 views)
File Type: jpg _MG_4480.jpg (38.0 KB, 52 views)
File Type: jpg _MG_4480IQ.jpg (67.8 KB, 31 views)
File Type: jpg Histogram.jpg (74.3 KB, 27 views)
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  #35  
Old 08-04-2014, 03:59 PM
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dtvmcdonald dtvmcdonald is offline
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One more piece of data. I took the picture in the last post of the
+I > -I and +Q > -Q transitions, smoothed out the dots, and
converted from RGB to Lab. Lab is similar but not identical to YIQ.
I rotated the UV axes to actually be as close as possible to IQ.
I then made grayscale plots of "LIQ" for (top three) the I transition,
and three for the Q one. These are in fact highly contrast enhanced.

These do show some cross-interference between I and Q and
also show the fact that I has wider bandwidth, though the latter is better seen in the thumbnail of the color pictures.
Attached Images
File Type: jpg Individual_Channels_c.jpg (57.1 KB, 22 views)
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  #36  
Old 08-04-2014, 10:15 PM
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old_tv_nut old_tv_nut is offline
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Wow - great detailed work.

I have a question about your +/-I and especially +/-Q signals:

When you filtered the Q, did you delay the Y to match? and did you also delay the I (less) to match Q? The magenta/green Q transition appears to be later than the Y transition (the colorless area is on the right side of the brightness step). If you turn down the color to get monochrome, where does the Y transition appear compared to the Q transition?
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  #37  
Old 08-05-2014, 12:58 AM
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ChrisW6ATV ChrisW6ATV is offline
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Some amazing work there! I am quite impressed.
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Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did."
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  #38  
Old 08-05-2014, 07:42 AM
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dtvmcdonald dtvmcdonald is offline
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Quote:
Originally Posted by old_tv_nut View Post
Wow - great detailed work.

I have a question about your +/-I and especially +/-Q signals:

When you filtered the Q, did you delay the Y to match? and did you also delay the I (less) to match Q? The magenta/green Q transition appears to be later than the Y transition (the colorless area is on the right side of the brightness step). If you turn down the color to get monochrome, where does the Y transition appear compared to the Q transition?
When I did the filtering, there was no delay. That is,
Photoshop left the center of the transition at the same "time"
for each channel. I don't
know if it is supposed to be done in the camera chain. What I
did would be correct IF the camera chain does the correction
AND the Blonder-Tongue modulator does not.

In any case, You can tell for yourself whats going on
by looking at the B&W images I
posted of the individual channels. Its visible in the original JPEG before being played. Attached. Note that the Y really IS unfiltered in
this file ... you can see that in Photoshop by converting to Lab.
Attached Images
File Type: jpg SatRGBEqualIQblurredmore.jpg (41.0 KB, 24 views)
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  #39  
Old 08-05-2014, 09:26 PM
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old_tv_nut old_tv_nut is offline
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Ah - I think I see the problem. You did the filtering for the source signal as some sort of Photoshop motion blur, correct? It is showing very sharp transitions into and out of the "blurred" area between the magenta and green. This is not normal filtering, and results in strange effects.

Here are some simulation results with proper filters in Photoshop. The simulation includes the modulation and demodulation, so cross-color (orange/cyan moire' in striped awning) and cross-luma (dots on vertical edges of the bars) are visible.

The smaller +/-I and +/-Q bars at upper left center have no Y variation, so you are seeing just the effects of I and Q there.

There is some anamorphic stretch due to adjustment to get the color subcarrier dots approximately correct coarseness.


Original:
veg market with IQ bars and cbars by old_tv_nut, on Flickr

chroma on gray with transmitter I and Q filters:
chroma in IQ filtered by old_tv_nut, on Flickr

Demodulated chroma on gray with both transmitter and receiver I and Q filtering:
chroma out IQ code + IQ decode by old_tv_nut, on Flickr

Demodulated I:
I out as mono by old_tv_nut, on Flickr

Demodulated Q:
Q out as mono by old_tv_nut, on Flickr

Final output:
final out IQ code + IQ decode by old_tv_nut, on Flickr

Both the cross color and cross luma are more visible than normal because they are stationary.
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  #40  
Old 08-07-2014, 10:41 AM
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dtvmcdonald dtvmcdonald is offline
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Last night I tried to receive our actual OTA real NTSC Ch. 39 and
failed. I also failed to find a radiated local oscillator signal at UHF with a
spectrum analyzer, though I see it at VHF. I should add that the signal
is weak, but works OK on other sets because there is a 16 dB gain
0.5 dB NF preamp. Could this be a weak oscillator tube? It tests excellent.

Are all of these CT-100s actually supposed to get UHF, or only
some of them?

Could bad blooming be due to use of a 1X2A rather than 1X2B? I forget
what I found in our old stock ... it tests good offscale.
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  #41  
Old 08-07-2014, 02:53 PM
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dtvmcdonald dtvmcdonald is offline
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Two more questions! When the picture goes absolutely totally blurry on an
all-white screen, is it the 19,500 volt HV or the focus voltage, or both,
that collapses? I suppose I could measure them, but with the chassis
in the set and turned on, I'm afraid of accidents.

I'm missing my horizontal and vertical hold knobs. The rest look
rather generic ... where do I get matching ones?
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  #42  
Old 08-07-2014, 03:13 PM
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Quote:
Originally Posted by dtvmcdonald View Post
I'm missing my horizontal and vertical hold knobs. The rest look
rather generic ... where do I get matching ones?
No knobs, these are just knurled shafts.

jr
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  #43  
Old 08-07-2014, 03:24 PM
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"Are all of these CT-100s actually supposed to get UHF, or only
some of them? "

Do you have the proper strips installed for the channel?

jr

Last edited by jr_tech; 08-07-2014 at 03:29 PM.
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  #44  
Old 08-08-2014, 12:09 AM
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Dave A Dave A is offline
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Doug will be getting a UHF strip from my collection. We have been in touch. And I have more if anyone needs one. Stay tuned.
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Last edited by Dave A; 08-08-2014 at 12:42 AM. Reason: text
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  #45  
Old 08-08-2014, 10:12 AM
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dtvmcdonald dtvmcdonald is offline
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Quote:
Originally Posted by jr_tech View Post
No knobs, these are just knurled shafts.

jr
REALLY? I find that hard to believe! These are user controls.

McVoy did, however, say "all knobs"
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