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.

Conrac was another brand of monitor in the tube era. If I recall they even had a color model in the late 50's or early 60's.

Conrac made 21 inch broadcast color monitors that were direct competition for RCA.
When SMPTE standardized the rare-earth phosphor colors for broadcast monitors, they settled on a unique batch that came from Conrac and became known as "SMPTE-C" standard. Three barrels of R,G,B were set aside and RCA made special runs of tubes to supply the broadcast monitor market.

Yup. I've got a conrac CYB-21 color roundy monitor (its supposedly the last roundy broadcast monitor model made) and a RCA TM-21 which was the first 21" roundy color broadcast monitor available and stayed in production long enough to be sold with 21AXP22, 21CYP22 and 21FBP22 CRTs

I need some fresh ideas here as the video input amp is really kicking my backside. The top trace is the output of my Tricaster with a chirp pattern going into the video amp, the lower trace is what I'm finding on the grid of the 6MU8 which has been disconnected from the set video detector and has a 470k resistor to ground. On the amp board the heaters and +285V are bypassed to ground via 0.01uf ceramics but it seems like something is ringing. Here are the images of the scope, these are about the best I can capture.

Thanks in advance for any insight, I'm close but missing something I'm not completely sure of.
Brett

Deleted links from this post, images on post below.

I'm getting 404 file not found on these.

Lets try this again using imgur.com

Input board
https://imgur.com/JJnWFXd

Colorburst signal expanded on Tek 465 scope, top is source
https://imgur.com/Fag4K42

Chirp signal, top is source
https://imgur.com/2Agk7k8

Well, I see the thick traces on the output, but can't tell from these if it's some kind of high frequency oscillation, just lack of DC coupling, or hum.

Are you using the circuit in broadcast news or something else?

Running the same circuit in the Broadcast News article on page 18 using the 12AT7. Looked at it much closer again on the scope and it's clearly oscillating so now I get to figure out how to best neutralize this without compromising the response.

Where is the termination? On the board or at the end of the loopthru (bnc tee)?
Try other cables. Is your scope on 20MHz bandwidth?
Ground loop between scope, bar generator, and/or TV?

Termination at the scope with another Tee and the scope at the full 100 MHz bandwidth (tek 465 10:1 350 MHz probe), I looked at the output with my R-2670 spectrum analyzer and it appears to be oscillating around 10-15 MHz depending on the input signal so I'm going to drop a shield around the tube itself and see where it goes.

Push that 20 MHz BW switch in and see if it doesn't clear up. I never ran my scopes at full BW at the TV station for obvious reasons. WHY do you need 100MHz BW for only a 4.5 MHz signal???

Actually my career was 2-way radio and that demanded a high bandwidth scope, even with the 20 MHz limit I can still see the ripple but as it stands now I have a good handle on the issue with a shield around the 12AT7. As it turns out the reason the color was washed out was because the 1st video amp in the set was being pushed to saturation so I'm going to add a gain control pot to its grid. The amp can pass 5+ MHz to the 1st video and everything I own is previous generation broadcast be it DigiBeta, DVCPRO and Type-C so bandwidth here isn't an issue, the picture tube begins to blur at the 350 horiz line point of the resolution chart so this is about the limit of the delta gun CRT but by no means the limit of the set itself when unleashed from the 4.5 MHz trap.

So after a few long nights with the soldering iron and sifting thru the parts bins... I think the picture speaks for itself. 1970 Magnavox T-940 AstroSonic on composite video direct from my Sony BVH-2000 Type-C with the four card internal TBC. The audio is very strong and clear, I'm still having some instability issues from the lack of video AGC so my next project is to integrate the existing AGC into the input video amp and adding an outboard sync separator like the LM-1881 to directly feed the horiz & vert, I have a dedicated house BB gen so this would be a bonus.

Here's the screen shot of INXS direct from Type-C. Nice to actually watch something on a real CRT.

https://imgur.com/7CNslBz

https://imgur.com/7CNslBz

Nice!

Video AGC??? Most monitors don't have that.
The best video AGC I ever saw was a TA-19 proc amp used in NTSC signal processing at TV stations.
It would make chicken salad out of chicken $#!+.

Video AGC shoould not be needed if you just set the gain at a fixed value for a 1 Vpp input (terminated).

Input value is 1V P-P confirmed by a Leader 5860C waveform monitor and it's terminated at the input amp itself. Problem I'm chasing is a lack of sync and high whites that's throwing off the 1st video amp of the set causing what appeared to be an overload condition thus my attempt to use the AGC to stabilize the input amp. Problem I seem to be having is a lack of DC for black ref and this is killing the sync. Picture one is the clean signal coming from the Phil Nelson 12AT7 input amp feeding directly into the pentode grid of the 6MU8 1st video amp. White is clean & sharp but the black is lacking, picture two is the output of the 1st video amp at the plate, the little overshoots are products of the sharpness coil on the end of the cathode. Picture three is the 1st video amp of the Magnavox itself, this has been completly isolated from the detector & 4.5 MHz trap and has a 470K grid resistor tied to ground. The Phil Nelson DC restoration circuit I'm using has the 22K resistor and 10uF capacitor that was described in the modifications. The big question I have is: what am I doing wrong here?

1st Image:
https://i.imgur.com/3jeOfbw.jpg

2nd Image:
https://i.imgur.com/Jvlb1kX.jpg

3rd Image:
https://i.imgur.com/85tGtdD.jpg

The input circuit with 1N34, 470k, lytic, and voltage divider to negative supply should supply the correct DC restoration level.

You should not add a resistor from the first video amp to ground.
Instead, adjust the value of the asterisked resistor to get a reasonable grid and plate voltage similar to what you get when the set is operating from its own video detector.

Also check that the p-p value of the signals is correct. If not, you may have to adjust the gain of your input circuit.

Would anyone here have any info on an RCA model JM-897W? I don't have a chassis number but it was used as a "professional monitor" during the 1970s

Thanks

Arc-tec, are you using AC coupling or DC coupling to go from your circuit to the TV?
That RCA model, I vaguely remember a set like that at a station in SC. Its rectangular and solid state if I recall correctly.

Everything is AC coupled via 0.22uF caps from the input to the circuit, between the stages and output before the DC restoration and that is directly coupled to the grid of the 1st video amp pin-2.

Someone slap me upside the head?!
I'm chasing my tail over the DC restoration totally neglecting the lost connection between the 4.5 sound trap and the input point of the 1st video amplifier... the brightness control is basically running wide open without a reference on the backside to provide the negative voltage it needs. I lifted R217 & R218 to bring the negative value back and everything fell into place.

Yes I shall humbly accept the dumb@ss of the year award and host the rubber chicken dinner.

Hehe, ouch, but s*&%@ happens everywhere, with anyone...