7jp4 DIY Television - Videokarma.org TV - Video

bhegges · #1 03-20-2011, 09:52 PM

As a kid I always thought it would be fun to build a TV. Once I grew up I went to school for Electronic Engineering, only to become an IT guy. Fast forward to today and I have finally put childhood ideas to work. I wanted to build a TV (it is really just a monitor) and something with octal tubes would make it even cooler.

The design comes from an Admiral 19A11. I substituted the 6au6 video amp with an octal 6sh7. Other changes include wiring in a retrace circuit. All of the tubes including the picture tube have 6.3 volt heaters which are wired in parallel. The power supply transformer was custom made by Sowter which supplies the 6.3 volt and 5 volt heaters along with the 250-0-250 volt main supply. I fabricated the aluminum plate and wood chassis myself. All of the wiring is point to point. If I was going to do it again I would have bolted in a few terminal strips to solder to. I found a NOS 7jp4 tube which provides a very nice picture which is nice and bright with or without lights on. I am pleased with the results, I would like to think this would have been the coolest diy project sometime back in the late 40s, probaly still cool today. Last thanks for all of the knowledge this forum provides, I have read and learned from the many threads.

Schematic

miniman82 · #2 03-20-2011, 10:29 PM

Nice, but I can't see it all. Can you shrink the pics?

Kevin Kuehn · #3 03-20-2011, 11:24 PM

That's really neat, very nice job!

Got any pictures with the screen lite up?

Kevin

cwmoser · #4 03-21-2011, 05:42 AM

That is super cool. If you can find the parts, looks like that would make an interesting kit. The market might be there but I'm impressed with you labor. Reminds me of the Emerson 639 TV I restored - it uses the 7JP4 tube too.

Carl

Sandy G · #5 03-21-2011, 07:02 AM

Wow...GREAT job !

Reece · #6 03-21-2011, 07:31 AM

That's just the sort of project I like. You did a super neat job. Thanks for sharing it. Can you show a pic on the tube?

wa2ise · #7 03-21-2011, 04:07 PM

Maybe you can change the horizontal frequency enough to make it display 720p (about 2.7 times the NTSC horiz frequency) or 1080i (about twice the NTSV horiz freq) B&W HDTV. Use the green jack on the "component" outputs of a HDTV receiver box.

That would make it a nice mix of vintage and modern. If the spot size is small enough, it could make a really sharp picture.

polyphase · #8 03-21-2011, 05:14 PM

Very cool indeed. I'm impressed.

Maybe the next step is to add color using the same 7JP4 plus a colorwheel.
Heres how:

http://www.hawestv.com/mtv_color/colrtel_block.htm

Electronic M · #9 03-21-2011, 05:28 PM

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 · #10 03-21-2011, 09:40 PM

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

Zenith26kc20 · #11 03-22-2011, 02:11 PM

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?

bandersen · #12 03-22-2011, 02:25 PM

I suspect they came from an Admiral 19A11. The CRT shield and HV cover sure look like they did.

cbenham · #13 03-22-2011, 02:57 PM

Quote:

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 · #14 03-22-2011, 07:13 PM

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 · #15 03-22-2011, 07:52 PM

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