Videokarma.org TV - Video - Vintage Television & Radio Forums - Add RCA Component Sound And Video Hook Ups

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- Early Color Television (http://www.videokarma.org/forumdisplay.php?f=36)

- - Add RCA Component Sound And Video Hook Ups (http://www.videokarma.org/showthread.php?t=263374)

NoPegs

02-04-2015 09:48 PM

Quote:

Originally Posted by Electronic M (Post 3125541)

though if the output amplitude is large one might need to use a voltage doubler, trippler, etc to get enough rail voltage for the OP amp....Not to mention the many other power sources both set derived and tacked in that could be devised.

Lets not forget the fact that these are all high impedance circuits. You could just make an "unun" transformer. So you have 1v p-p composite in, and you need 10v p-p out? 1:10 matching transformer. Phase inversion is easy if you use a 1:1 isolation transformer (There are many made just for video.) and flip the output phase. You can also combine both. Invert the phase and derive 5v p-p baseband via a swapped output 1:5 ratio unun.

dano	02-05-2015 09:50 AM

That's a good idea, and I guess that raises another question that I hadn't thought of. Does the composite input need to have a 50 ohm termination? I haven't worked with video inputs very much, so I'm not sure what would work best. The unun transformer is a good idea, it might also be useful for a hot chassis set. Without some form of isolation, I don't think it's a good idea to add such an input to a hot chassis set.

NoPegs

02-05-2015 07:18 PM

Quote:

Originally Posted by dano (Post 3125599)

75 ohm termination is good engineering practice for CVBS. That was a very good question to ask. Means that you're understanding things. :thmbsp:

Electronic M

09-01-2015 01:00 AM

Quote:

Originally Posted by damen (Post 3123428)

I had success with my Zenith 29jc20 set I got some help from my friend Danny and we made it work. It makes a better picture and seems to have eliminated interference I used to get which is bad at my present location and the tuner can be on any channel since it has been bypassed. No more need for a converter box to and if they ever bring back the VHF tuner I can put it back the way it was. Some how I doubt that will happen. The bar on the screen of the TV is from my camera in the picture I added. I may try this on a RCA next.

I'm about to try this on my 29JC20 as workaround for it's alignment issues. If I get stuck do you have any schematics marked up with the mods? Also are the coax leads all you did?....I'd presume something was done to disable the RF system like removing B+ or IF leads from the tuner or removing the tube prior to the first signal injection point.

DavGoodlin

09-01-2015 07:45 AM

1 Attachment(s)

Quote:

Originally Posted by wa2ise (Post 3123496)

I think you'll see the biggest jump in image quality if you can modify the set to accept "S video". That's separate luma and chroma, not mixed together. This would be non-trivial to do, though, you need to find the chroma luma separator (usually some sort of LC trap or bandpass circuit). Then you have to inject (with the right amplitude and polarity) the luma into the circuit that received the luma from the separator, and chroma the chroma.

As for hot chassis sets, an isolation transformer would be best, but be careful where you install it, to keep stray magnetic fields out of the CRT.

This was from a thread, I thought was yours:scratch2:Attachment 187919

wa2ise

09-01-2015 12:27 PM

Quote:

Originally Posted by DavGoodlin (Post 3142361)

This was from a thread, I thought was yours:scratch2:

http://www.videokarma.org/attachment...hmentid=187919
That will work to create composite video that will have minimal cross luma into chroma errors in a notch filter color TV set. If the TV set in question is a notch filter set, the luma bandwidth that you see on the CRT screen is low pass filtered to avoid the appearance of the chroma subcarrier (a crawling fine grain checkerboard pattern atop highly colored areas of the image).

True S video would produce about twice the resolution than the above composite video maker. But this composite video lets you not need to dig deeply inside the set's color circuits.

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