Video inputs Tube TV
 

Does anyone recall what the chassis or model was of a late 60s vintage RCA that had the SO-239 video in/out & 8-pin jacks used by schools and the like? I had one years ago that was used with a Panasonic EIAJ format and I recall some of the big ugly presentation Something Carlson 25" B&W with big knobs and speakers had a video I/O jacks. What I'm specifically looking for is the interface circuit they used to bring the video in behind the detector and sound trap to use in my Magnavox T940 and maybe someone knows of other models that had the video in/out.
I was the A/V geek in school during the 80s and spent plenty of time messing around with these but for the life if me I can't remember the models. The RCA was a metal cabinet 20-something inch and the Something Carlson was a big wood affair we called the "rolling tombstone" being so big and bolted to a tall wheeled cart with a Panasonic NV-3020 EIAJ... we were slightly behind the times and didn't get anything VHS until around 1983 and that got us some of the XL-100 Lyceum sets.
I've spent the better part of an evening looking for potential tube sets with the video in/out but keep striking out, anyone maybe have any ideas?

Thanks
Brett

Can't help you here, much. I was AV in HS in the early '70s. It's Setchell Carlson...

I've never seen the RCA service literature for the "Lyceum" sets. It wasn't included in our standard RCA literature, had to special order it. I know one model, JM-897W was a metal cabinet CTC-38 using chassis version number CTC-38XE. The interface circuit board for the AV connections had an RCA part number of 130429. There is a Sony black and white set, model CVM-2300U, that is covered in Sams Photofact set number 882, folder number 3 that appears to be an Emerson tube chassis TV with a Japanese sourced AV input board using 6 transistors and a relay for selecting regular TV or the "Videocorder Socket" it has.

Guess I have to think outside the box on this one, I had a CTC-38 as a New Vista Color years ago but didn't know it was used for the Lyceum. Talked to a buddy who works at the Mpls Public Library that has the Sams Photofacts and he struck out on the XE as well but found the F3/882 but it's transistor as you mentioned and in very poor condition.

There was Setchell Carlson and Stromberg Carlson, our schools had both and they were equally ugly but I'm sure it was the Setchell Carlson as recall seeing the St. Paul Minn on the label.

I have time to get this one together, the Magnavox needs a full alignment of the IF and chroma before I can do anything else. Last time the set ran was the summer of '06 and I attempted to align the IF & chroma using a Sencore SM-152 marker generator that I didn't know was malfunctioning after replacing numerous bad resistors further compounding my problems. I've since acquired a Heathkit IG-57A with the book and verified it with my Motorola R-2670 service monitor.

I will journal the resurrection of the Magnavox as my brain and time permits, mechanically everything is sound and the pix tested just under 1.6 ma cathode on my 467 according to my old notes but the front CRT mask is stress cracked on the right side in the middle so everything had to come out for the repair. Going to pull it together as best I can with straps and poly glue dowels on the inside to reinforce and stabilize then shoot the outside with a dull silver as the original has turned a shade of green. The stereo portion was never that good and the turntable always seemed to run a little slow so they will be addressed in time. I replaced the original amp with a Heathkit AA-100, the original was smoked in the mid-80's when we got a little carried away with the volume and bass and after this the set was hidden away until I tried to resurrect it around 2005, now it's time for another try.

I have one of those monochrome Setchell Carlson sets you describe (I'll add the model number when I get home), and a color industrial monitor rebadged as a SONY (I believe it was special ordered as a video tape monitor for a trade show) there's a thread on it here...As well as 2 Setchell Carlson consumer tube color TVs. The color monitor uses the same chassis and tube modules as a rectangular color TV only they eliminated the tuner IF and sound modules. SC designed their IF modules to output line level video at the detector so the 3 video inputs go to a selector switch then directly to the video amplifier module without passing go or collecting $200...
Many sets were like that by the mid 60s, but there were some still that weren't.

I think I saw that circuit on worldradiohistory.com It use a 12AT7 as a preamp and cathode follower. Are you trying to add that to an existing receiver?
I chose the solid state route. Its easier than you think.
The left module is for a Heathkit and the right module is for RCA
They're built totally different. One uses a video op amp and the other uses 2 bipolar transistors. Connect after (or remove) the sound trap. You could put in a switch or relay if you want to use the RF input as well.

So I cheated and made an amp/buffer using transistors and that got me the needed gain to drive the 6MU8 1st video amp section, now its just a matter of tweaking things to flatten the response and the input gain. So far it's responding well but has some fringing that appears to be a high frequency ring and the scope shows some leading overshoot but I'm confident this can be overcome.

Will post my results as time allows.

Thanks for the link to worldradiohistory.com, I completely forgot about that site.

I removed the sound trap on both since these would not be used as receivers anymore. The sound trap is a real problem. It creates all kinds of group delay problems at the upper end of the video passband.
For the video op amp I used a MAXIM MAX405 which may be hard to find in a DIP package these days. At one time, you could call MAXIM on their 800 number and they would send you a couple FREE.
Another video op amp I like is the Analog Devices AD828. Seems to be a current product.

Might have to look in this direction as I'm having some real issues with the high end and chroma. Don't know if this is an impedance issue as I've worked both sides of the matching network and removed the 4.5 trap, Still looking for the tube circuit that RCA used and have spent several hours poking around the worldhistory.com site for this.

Phil Nelson posted the RCA tube video input circuit for the CT-100 on his site if that is what you are looking for.

https://antiqueradio.org/VideoAdapte...Television.htm

Or here:
https://www.worldradiohistory.com/AR...ews/RCA-89.pdf

An interesting pdf can be found here:
https://www.st.com/resource/en/techn...lectronics.pdf

Good deal thank you for that. I'm still chasing my tail with the video input circuit but I did find the name of the Setchell Carlson TV-Monitor we used in school (before climate change) and they were called the "Color Educator". For some reason I thought they were B&W but as it turns out it was because they were used with a Panasonic NV-3020 monochrome EIAJ machine and that added to my confusion.
Problem I'm having seems to be with the impedance matching and higher frequency response as the chroma is very weak, strong color highlights show but anything below that is washed out luma only. Going to put together that 12AT7 circuit tonight and see how that works out, not sure I have a 20uH choke however.
I spent the morning looking at the World History pages but didn't get this far down the list so thanks again for the link, I didn't know we had microwave STL in the early color days. Judging by the cabinet it looks like a kilowatt or better of input power to get a few watts of microwave, wish we had those electric rates today!

Setchell Carlson made B&W school monitor TVs I have one..Model 2100 SD. They also made industrial color monitors (also have one). I didn't know that the they made a school version of the color monitors but that makes sense.

Didn't know about the industrial monitors, they're built tough enough I'd say.

So the video input amplifier was a bust, everything was built to the schematic including the 1N34 but the Magnavox isn't happy with the addition. The issue is it seems not enough of the chroma signal is passing thru and this is causing most of the color to wash out. The amplifier bandwidth seems to be good as I have tested it with a sweep signal and it rolls off only slightly just over 5.5 MHz. Colorburst is strong but the color itself is lost except in the saturated areas, 75% colorbars seem to have a lag to the leading edge and they bleed over into the next bar, I forget the technical name for this. Running the set with RF has good color.

I've tried uploading images with zero luck, the best I can do is a 50k image file and that doesn't show the needed details, if I can't get the server to accept them I will do a quick vid and post it on YouTube as words can't accurately describe the issues, honestly I need a fresh set of eyes and some ideas here and any help would be appreciated.

Thanks to all
Brett

Sounds to me like the DC bias may be wrong for the TV's circuit, if you can measure good response in the amplifier alone, but something is happening to the chroma when feeding the set.

Especially if the burst comes through OK, but chroma up in the active video voltage area is being mangled somehow.