Prototype set is here

[tubesrule]

Terry,

The CPA chroma frequency was defined as exactly 495/2 * Fh. Using the original Fh of 15,750.00Hz yields exactly 3,898,125Hz. This also means that there was an exact relationship between the phase of the chroma carrier and the line frequency (i.e. the phase and position of the chroma carrier will be exactly the same on every other line). From what I have read there was no half line offset. That's something that came later. Of course anything can be done now, but I would recommend putting the set back to as close to original as possible, warts and all, to verify what they saw during the original tests. This will result in a stationary, visible pattern but that's what they would have seen.

So using the current NTSC line frequency of ~15,734.27Hz and the same 495/2 yields ~3,894,230.77Hz. This means that to maintain the same locked phase relationship between the chroma carrier and the line, we would have to use this new frequency. If we wanted to use the original 3,898,125Hz, we would loose the locked phase relationship between the chroma carrier and the line. This will change the visible dot pattern.

The issue with the SCRF converter is there is no frame memory, so rate conversion cannot be performed. The line output timing would match the line input timing, or 15,734.27Hz. With the WC converter the output is complete independent of the input and anything can be done.

So is there a design reason to have the chroma locked to the line, or does it even matter with this set? Do we want to observe the set exactly as it would have appeared during the tests? Since a crystal will need to be cut it could easily be cut for either frequency, or both could be cut and tried. To the converter it's just firmware so it doesn't matter. This will ultimately be Nik's/Steve's call assuming they take the set all the way to operation on CPA.

Darryl