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  #301  
Old 10-01-2011, 04:29 PM
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John Folsom John Folsom is offline
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Nick, examine the HV winding on the flyback carefully. Often the failure is at one end or the other, where it might be possible to repair. Another option is I could wind you a new HV winding. Give me a shout if you want to discuss the possibilities.
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  #302  
Old 10-01-2011, 04:46 PM
DaveWM DaveWM is offline
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could it be a transformer and not an autoformer?
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  #303  
Old 10-01-2011, 04:47 PM
Mal Fuller Mal Fuller is offline
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Quote:
Originally Posted by John Folsom View Post
Nick, examine the HV winding on the flyback carefully. Often the failure is at one end or the other, where it might be possible to repair. Another option is I could wind you a new HV winding. Give me a shout if you want to discuss the possibilities.
Now there's an offer that Nick isn't likely to take a pass on. I'm very impressed to consider that the HV winding can be fabricated and replaced.
I'm standing by to follow this saga.
John, photos would sure be a treat for everyone.

Last edited by Mal Fuller; 10-01-2011 at 04:49 PM. Reason: Improve layout
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  #304  
Old 10-06-2011, 02:13 AM
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Originally Posted by miniman82 View Post
Quick question: this chassis has a control labeled 'Horiz Phase'. Anyone have any idea what the purpose of this control might be?
It could be literally what it says, which on many monitors I have used is essentially a horizontal centering control. Its function would be to center/position the video within the horizontally-scanned area on the CRT.

From your description of the circuit, this second possibility seems less likely, but if this is indeed a CPA chassis, could the phase control function as a tint/hue control?
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  #305  
Old 10-06-2011, 02:36 AM
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If it's CPA, there would be no need for a hue control since the CPA was meant to cancel out color phasing errors. It might be something to do with centering the video in the frame, but it has a proper centering control to center the actual scan so I'm not sure what to think at this point. If Ed would get off his duff and email me those scans I might have a clue...lol
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  #306  
Old 10-06-2011, 04:04 PM
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Phase if horizontal could refer to burst timing

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  #307  
Old 10-11-2011, 08:35 PM
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I guess you already have enough cabinet choices, but I thought of your prototype when this popped up on the local CL, as its grille resembles the CT-100 cabinet. It's much too shallow, however -- lacks about 6 inches.

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  #308  
Old 10-11-2011, 09:01 PM
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Originally Posted by miniman82 View Post
If it's CPA, there would be no need for a hue control since the CPA was meant to cancel out color phasing errors.
CPA works at the vertical rate, not horizontal. One field is one color phase and the second field is the other color phase. CPA was dropped because in it's simple form it produced bad flicker at the vertical rate. There were no 'one field' video delay lines available to solve the problem at that time.

Cliff
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  #309  
Old 10-11-2011, 10:48 PM
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Originally Posted by cbenham View Post
CPA works at the vertical rate, not horizontal. One field is one color phase and the second field is the other color phase. CPA was dropped because in it's simple form it produced bad flicker at the vertical rate. There were no 'one field' video delay lines available to solve the problem at that time.

Cliff
Very true. The problem was that the NTSC system was not true constant-luminance because of the CRT non-linearity. (Current digital TV systems are not constant-luminance either.) What this means is that the chroma signal can affect the brightness of a color (more so for saturated colors, not at all for grays).

It's the chroma flicker translating into luminance changes that is visible. During the development of HDTV, Dr. Schreiber at MIT proposed going to a true constant luminance system, and demonstrated that 30 Hz true chroma-only flicker (or even 15 Hz!) is invisible. This could hypothetically be used to reduce the frame rate of chroma to save bandwidth, but would run into problems when the camera pans or the eye tracks a moving object. It also could be used to more crudely encode the chroma without producing visible artifacts.
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  #310  
Old 10-20-2011, 10:03 PM
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Finally got around to making a base cover for the HV rectifier, now maybe it won't break so often from bouncing around. It's just a section of poly that I cut from the center of an old wire spool, I was gonna use a pill bottle but couldn't find one the right diameter.

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  #311  
Old 11-27-2011, 02:55 PM
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Tom C. found the plug I need for the filament string in this chassis, I hope to have it in my possession by the end of the coming week. Now, if only I could source a backshell for the other plug...

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  #312  
Old 11-28-2011, 01:42 AM
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Originally Posted by miniman82 View Post
Tom C. found the plug I need for the filament string in this chassis, I hope to have it in my possession by the end of the coming week. Now, if only I could source a backshell for the other plug...

What's the diameter of the connector? I may have a shell for it.

Cliff
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  #313  
Old 11-28-2011, 02:51 AM
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Originally Posted by cbenham View Post
What's the diameter of the connector? I may have a shell for it.
I get 1 3/8" for outer diameter, not sure what the shell size should be. Steve McVoy sent one from a regular octal connector, it was too small.
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  #314  
Old 11-29-2011, 01:11 AM
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Quote:
Originally Posted by old_tv_nut

It's the chroma flicker translating into luminance changes that is visible. During the development of HDTV, Dr. Schreiber at MIT proposed going to a true constant luminance system, and demonstrated that 30 Hz true chroma-only flicker (or even 15 Hz!) is invisible. This could hypothetically be used to reduce the frame rate of chroma to save bandwidth, but would run into problems when the camera pans or the eye tracks a moving object. It also could be used to more crudely encode the chroma without producing visible artifacts.
The thought of true constant luminance is intriguing. Unfortunately, the benefit of transmission noise suppression in the blacks would be lost as the gama curve happily compensated for it. Not to mention the complication of adding a CRT compensation circuit at the receiver and having to reconcile some sort of backward compatibility if a fully constant luminance system was achieved.

With regards to the hue control critical adjustment, I recall working with "Simple PAL" receivers. The Delay PAL Monitors in the BBC studios had a simple PAL switch. It was great for checking PAL chroma subcarrier phase because an out-of-phase condition would yield "Hannover Bars". Each alternate line would have a noticable hue difference and even a slight phase misadjustment was very annoying. I would certainly prefer to see a noticable NTSC IQ system overall hue error to having to put up with the Hannover Bars. And this was the UK systems which allowed fully symmetrical upper and lower chroma sidebands which should eliminate the quadrature crosstalk problem! (Remember the UK channel was 8MHz wide with the sound carrier at 6MHz instead of 5.5MHz for their continental cousins. This allowed full +/- 1.5 MHz chroma bandwidth).

CPA was chosen as a means to help widen the chroma bandwidth (hence chroma resolution) and the Phase Alternate Line or Field was to help cancel the quadrature crosstalk resulting from the highly non-symmetrical chroma channels. Even with the hue control set to minimize the flickering, the flickering I would expect to be very noticable. In fact I would guess the hue control adjustment to be more critical for CPA than the later IQ system. It is which ever suits you: a slightly wrong overal hue versus a maddening flickery picture. (I, of course, use the term "hue" control loosely: it is the subcarrier phase adjustment I am referring to).

Last edited by Penthode; 11-29-2011 at 01:14 AM.
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  #315  
Old 11-29-2011, 02:38 AM
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cbenham cbenham is offline
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Originally Posted by miniman82 View Post
I get 1 3/8" for outer diameter, not sure what the shell size should be. Steve McVoy sent one from a regular octal connector, it was too small.
I misjudged what is in the picture entirely. Thought it was a small two pin 1/2 inch diameter Cinch-Jones connector, not something 1-3/8 inches diameter.

I'll look some more but I doubt there's anything like that in my parts boxes.

Cliff
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