7jp4 DIY Television

[Electronic M]

You and I think alike wa2ise. I was wondering how good such a mod might be on a color TV some time ago. I first asked the question after trying to connect an old windows 98 computer to my 71' Zenith Chromacolor through a VCR. The set up was very crude, consisting of me sticking wires into the VGA jack and using clip leads to connect those wires to the yellow composite video jack on the VCR. By adjusting the hold controls I was able to get four synched monochrome images with a big cross hatch in the center(like some screen shots of CBS color telecasts on NTSC sets). I gave up on this because I did not feel comfterable modding the TV at the time, did want to build or buy the circutry to allow for color, have no idea of how to get arround the auto VGA out shut off caused by (I presume) lack of the digital signal a monitor would normally send to the computer, and said to my self my colege is going to give me a computer next year so i do not really need to resurect this dinosaur.
But in a use with HD light this mod becomes interesting again!

Tom C.

[Don Lindsly]

The contrast control is innovative in that it compensates for sync level changes with contrast setting. Clever!

[Zenith26kc20]

I'm curious... where did the "special" parts come from (flyback, vertical blocking oscillator transformer, horizontal parts, etc). Love the idea of building one. What kind of video bandwidth does it have?

[cbenham]

Originally Posted by Electronic M

You and I think alike wa2ise. I was wondering how good such a mod might be on a color TV some time ago. Tom C.

If you want to add a color wheel, check out this project by pielock373 over on the Antique Radio Forums for some 'how to' answers and good ideas:
http://antiqueradios.com/forums/view...299b1ae46c2828

Cliff

[bhegges]

Thank you everyone for your kind comments.

bandersen, you are correct, all of the “special” parts came from an Admiral 19A11 chassis. The horizontal & vertical blocking transformers, the high voltage coil and cage along with the crt shield. Also I could not find potentiometers with the high voltage ratings for the focus, horizontal & vertical centering controls.

Some very early research proved these parts would be hard to find on a design build project. The next best step was to “steal” from an existing chassis and design. I know with radio design manufacturers seemed to zero in on the AA5 design, I wonder what about a design for TVs. Did Admiral get it right with their 19A11 or is there a better design for the 7jp4. The one thing I will comment on my TV project is that I seem to need to adjust something every time I turn it on.

[Phil Nelson]

Let me add my compliments on a very interesting and tidy looking project.

I'm not competent to review 7JP4 designs, but if you are curious about comparisons, you might want to include the National TV-7. The build quality is certainly nice and I believe it has DC restoration, something not always seen. The schematic is available at ETF:

http://www.earlytelevision.org/tv_sc..._diagrams.html

Regards,

Phil Nelson