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/VideoAdapterForRCACT-100Television.htm

Or here:
https://www.worldradiohistory.com/ARCHIVE-RCA/RCA-Broadcast-News/RCA-89.pdf

An interesting pdf can be found here:
https://www.st.com/resource/en/technical_article/ta0310-high-speed-operational-amplifiers-for-75ohm-video-lines-stmicroelectronics.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.

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.

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.

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.

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...

Congratulations! Yeah, I used to work on Micors and Mocom 70s converting them to 2M and 440. My Iwatsu 5702 scope was good enough for me. Why don't you post the final schematic for future reference?
Yeah, you'll like video AGC. Its like watching a movie at the theater. It's the same brightness all the time. It takes the highest value of luminance and makes it 100%. Doesn't do anything to the chroma.
You can probably build one with an optocoupler. You have to filter out the 3.58 before going to the luminance detector.
Probably some circuits on this here web.
When I was at the SC station with the TA19, the cable TV guys always said we had the best looking picture on the air.
And we always had beer in the transmitter building refrigerator.

I will and the mods needed for the T-940 to make things work happily together... once I figure out that secret formula. As it is now there's still some instability in the overall black reference but I'm confidant this will be overcome, I'm going to add the LM-1881 sync sep to the mix for a number of reasons one is to get a cleaner sharper timing signal for overall stability and the other is to use the composite sync output to trigger a black reference gate, this has turned into quite the project.

The biggest gain was changing out the existing 150 ohm cathode resistors on the input amp to 200 ohm pots in lieu of padding the grids, was able to vary the gain without saturating. Far too much drive from the input amp going into the 1st video of the 6MU8.
I will post more as time allows.

Someone slap me upside the head?!

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

Don't feel too bad. At least you didn't break anything...a couple of weeks ago I was quickly restoring a Sylvania Halolite so I could sell a second place holder model Halolite. I got it working great, then decided to transplant into it the remote control parts from the place holder. In the course of doing so I lost the series heaters, tried a bunch of stuff, including bypassing the heater thermistor (which made a new lytic pop and vent), gave up for the night then next day discovered that I connected the ground strap that connects the 2 chassis to the one large piece of metal that's isolated from the chassis...A connection point swap and a new lytic later and I was back in business but I sure felt stupid... Especially in light of observing that part was isolated about an hour before I inadvertently clipped to it...

So some progress has been made on the T-940, I cleared off the remains of the video IF strip back to the 1st video amp leaving a single 9-pin socket behind and built the input amp on the bottom of the board. the result is far less ringing and slightly better HF response, I also replaced numerous resistors on the video/chroma board as many were outside their tolerance. A 680 ohm measured 44 ohms and a 330K measured over 500K.

Going to AxMan surplus today for a handful of 7812's and other pieces to make the LM1881 sync separator, if anyone is familiar with the cities surplus scene they know what it's all about, rows of parts much of them NOS going back to the 1960's plus hundreds of new vacuum tubes for $2.50 each. They've been around since the 1960's and have most everything to support the older electronics.

Whoa! I found 2 video AGC chips you might be interested in. They are the MAX7452 and the AN3916. Never used either of these chips so I don't know much about them. The Maxim chip is available only in an SO-EP package- which, I think, is quite small. The AN3916 is a sip package. Both operate off +5. Both could be used for future video input mods for analog TV's. The AN3916 has an H OUT pin.
Maxim used to be quite liberal for free samples but they are now owned by Analog Devices who might be anal about it. I saw both chips on Ebay.
An interesting PDF: https://www.analog.com/media/en/technical-documentation/application-notes/an57fa.pdf

Thanks for the heads-up on those. Analog Devices is not exactly sample friendly as I've found out but I've had good luck finding what I need on the 'bay.

Just an update; I added the LM1881 sync separator to the Magnavox with mixed results. Vertical is rock solid and it takes almost 40 degrees of control rotation to break the lock but the horizontal is being rather finicky with respect to the signal phasing. If I flip the phase the horizontal locks but the color is off by 180 and is very unstable, running in-phase the color is good but horizontal is skittish. A work in progress... little progress.

Another chip that shows promise is the LM359. It comes in a dip package, is affordable and plentiful. It operates off a 12V single supply (requires a-c coupling) , bandwidth is 400 MHz, and has an 18 ma. output. 18ma. output is important since it takes 13.33ma to produce 1Volt into a 75 ohm load. It does not have AGC however but there are TWO op amps in the chip.

BTW... the original sync separator is poor with the video input amplitude?
Or is difficult to use/unstable with mod?
I had some issues with vertical when injecting video input in some old TV's, due to some issues. Some sets needed some different layout/some changing for sync separator. But the one most perfect one resulted to be a tube one, since sync separator is after the video output. Textbook perfect sync separating (for a single stage), with a 6CS6.
For my delta gun one, from the TBA IC's era, I used the LM1881, due to horrible verical behaviour of the original sync separator.

More progress on the video inputs today and the sync separator has pulled everything together, I had to do an NPN inverter on the composite sync line from the LM1881 and feed that to the horiz AFC while feeding the vertical sync to the vert section at R515 thru an 0.1uf cap. It's enough to trigger the MV and has a 2/3 swing on the vert hold control before it breaks lock.

The actual video input circuit is Phil Nelson design but with 500 ohm pots on the 12AT7 cathodes and 0.047uf cap between the stages, it then feeds the 1st video amp of the Magnavox which now runs a 6GH8. The 500 ohm pots help get the levels spot on without overloading, not every set will need the high drive level and these will eventually be replaced with fixed values once I have them dialed in.

I'm still dealing with the banding and DC restoration issues and not exactly sure how to solve this. It's very similar to when the RF AGC is too high.

I've been following this with curiosity, because I don't understand why an added sync separator is required if a video jeep circuit is properly designed to provide the peak-to-peak and DC levels required by a TV chassis. "Banding" (whatever you mean by that) and appearing like the the AGC is too high are signs that the basic input circuit isn't right.

Being a compost input it doesn't need the AGC to control the overall gain of the first RF amp. The issue here is the Magnavox T940 was never designed with the external composite video input in mind and everything was taylored to work together this one reason for the external sync separator as it's not so finicky with the variations of the levels and line voltage which would normally be countered by the AGC.

I agree oldtvnut. I have never had to add a sync separator to any circuit I built. Composite video has all the timing you need.
I'd like to see his schematic for all this.
Two other chips, that may be hard to find are the CA3450 (by RCA) and the HA5004 (by Harris). They have high output drive but both require a bipolar power supply.

Being a compost input it doesn't need the AGC to control the overall gain of the first RF amp. The issue here is the Magnavox T940 was never designed with the external composite video input in mind and everything was taylored to work together this one reason for the external sync separator as it's not so finicky with the variations of the levels and line voltage which would normally be countered by the AGC.

Thanks. I see this makes sense as the jeep circuit DC restored output is probably not following B+ variations the same as the set's video detector. However, I would be curious to put the whole thing on a variac and investigaate what the variations are, to find if it's possible to make the jeep circuit work by itself.

LM1881 with an NPN based inverter feeding the horiz AFC. I'm not sure if something was missed in the string of posts but the circuit is only to work in place of the original sync separator not to generate sync. The one issue I'm dealing with is the capacative coupling of the "Phil Nelson design" video input interface amplifier posted on page one of the thread and the lack of both DC restoration and linearity needed for the Magnavox separator to work correctly. The LM1881 is fed right off the 12AT7 input amp and breaks down the vertical, horizontal and burst/back porch to their own outputs, there is a timing resistor/capacitor that is used to set the pulse widths and this has proven to be an asset with unstable sources like VHS tape that doesn't pass thru my TBC, it also stabilizes the vertical during DVD playback so it's not affected by the Macrovision garbage in the blanking bar.
I did post the schematics back a few, they're links to the outside host imgur.com as videokarma will not allow me to post anything large enough for the needed details, I will post more progress pics and screen shots once I find my USB cable.

Okay time for a much delayed update on the T940 video input progress.

I won't say the set is complete by any means but it's good enough to watch. I completed the LM1881 sync separator board and have successfully interfaced it to the Magnavox. Original vertical feed resistor (R-515) was removed and this is where I feed the separator via 0.047uf 400V capacitor reduced from the 0.1Uf, the multivibrator triggers off the edge anyway so it's not super critical but too large a cap caused a retrace and foldover at the top, vertical output tube is a 6GF7 twin triode. This arrangement gets me almost 40 degrees of swing on the control before jitter and will not fully unlock going low, it also maintains a full lock with a macrovision signal.

Horizontal uses the composite sync out of the LM1881 via NPN inverter 2SC945 and feeds the original 6GH8 sync separator via emitter thru a 0.1Uf cap. The LM1881 follows the recommended layout from Texas Instruments and uses a 1-meg pot to set the pulse widths. Horizontal stability is very good and it's tolerant of timebase errors of home grade VHS sources. Everything I have is slaved to a master Videotek STG-6000 reference, playback formats are DigiBeta, BetaSP, DVCPRO Type-C and Newtek TC-550 Tricaster so timebase errors are not an issue.

Once I had the sync separator in place a few new issues came up with the chroma, color killer and 3.58 osc itself and I ended up replacing all of the 1/2 watt carbon comps on both the video and sweep boards as most were well outside of their 10% and 20% tolerance. I also cleared off the video IF board and it was repurposed for the 12AT7 input amplifier that was described earlier. Response is far more linear without the ringing I had earlier and it's passing better than 5.5 MHz of luma, still having issues with the chroma washing out on the highlights and I'm not sure what is responsible for this. I spent over 6 hours working with the bandpass and other coils for the chroma circuit but I'm still at a loss. At first it appeared to be a saturation issue with the input amp so I added 500 ohm pots to the cathodes of the 12AT7 to soften the gain but the less saturated areas seem to wash out of any color regardless of the luma. Plenty of room with the color level control but even at full drive the less saturated areas wash out to B&W. Burst amp and the related are all keyed correctly as the horizontal is timed ahead of the input amp and the pulse width is allowing the full burst thru without opening the bandpass amp late.

Other issues. Convergence has been a pain with what appears to be a harmonic of the horizontal leaking into the blue, on setup the blue has a distinct wave over the red & green which are flat and I'm at a loss for where it's coming from. Everything will converge with the controls but that wave or warp leaks into the blue horizontal line. Diodes all check good and everything responds well when adjusted.

Overall it looks good enough to watch without complaint and I've buttoned the back on for the time being, I have countless hours into replacing resistors and scrubbing off the rosin flux from the board in between the recent tornadoes we had, over a dozen trees damaged or completely uprooted plus a pine that broke the trunk and ended up upside down in the V of a nearby mature oak. It took over a gallon of gas and burned up two chains on a Stihl 024 chainsaw to slice this one up. No injuries or property damage but that pine was a priority removal.

So here are the links to the images for your entertainment, I've kept the resolution high as I don't feel like spending hours in GIMP to squeeze them down. They're large and detailed.


LM1881 sync board https://imgur.com/QY3eEc6

Repurposed Video IF board https://imgur.com/QXyJRES

Image in operation https://imgur.com/NWea574

Front Perspective https://imgur.com/PuzCXkv

I have numerous other images of the set & progress posted on imgur.com, search for images by brhatweed to see them all... I'm being lazy tonight. The link: https://imgur.com/gallery/magnavox-t940-astro-sonic-combo-console-shuTJoT

That's a pretty set. Hope you can keep sweep tubes in it. I'd put a couple of fans on the back cover to keep it running cool and prolong set life.

Thanks. I have a small EDM-Pabst whisper fan running on the bottom pushing a draft up thru the chassis and the other holes are covered with cardboard, it's strong enough to feel coming out of the cabinet back and the internal temp is down a good 20F according to my Fluke type-k thermometer.

I do have a good supply of 6LQ6 sweepers plus a number of the 6LF6 and 6LB6 that would only require a socket and screen resistor change if needed. The bigger problem I've been having is with gassy damper tubes, two have failed recently with one taking the primary fuse out. Most of my used tube stock goes back to the 1980's but the most recent 6DW4 was a NOS pulled from the carton and dated 1977... new when I was in the 3rd grade. We have a big surplus store called AxMan in St. Paul that has a good stock of NOS TV types for a couple bucks each so I'm going to grab a handful of those and the 6GH8s. They even have NOS 6CW4 and 6DS4 Nuvisters if anyone is interested, I'm not looking to make a buck just cover the purchase and postage and I'm open to trades.

New thermal issue has cropped up, takes a few minutes for the horizontal to drop down in frequency enough for HV and sweep, I suspect one of the "new" resistors is bad but it's not running the horiz output in full conduction from a lack of drive. Other issue is the color killer seems to also have a thermal problem killing the chroma until things warm then it returns to full saturation, guess I need to invest in a can of R-152 known as keyboard duster.

It's been quite a journey and honestly I didn't think it would still be going to this day, a one owner set from 1970 still in the family? Might just outlive me.

What year is that set? How much was it when new?
My mother had a Sylvania entertainment console years ago. It was hybrid- solid state RF, IF, and video. Tube type sweep. It had a phenomenal sounding AM radio! I think she liked it more for the furniture appeal. I remember changing some caps in it.
I made a board for the LM359 but the chip is on a slow boat from China. I made some changes to the original circuit. I changed the gain from10x to 2.5x and installed a pot for fine adjustment. Also I installed a trimmer cap to adjust the response somewhat. Its a 12V chip but I'm hoping it will work on 9V.
Another chip that might be useful is the LH0002. Its really not an op-amp but a buffer. It comes in a 10 pin dip and operates off a bipolar supply. There is also a TO-5 can version available.

The magnavox arrived about 9 months after I did in 1970 and I have no idea how much it cost. I was told it was on a "clearance sale" at a dealer on Lake & Cedar. It was quite reliable through the years with only the sweep tubes being replaced, might have been a 6GH8 or two and has countless hours of Saturday morning cartoons, football games and by the 1980's ATARI-800 time until it was replaced with a Zenith S-3 sometime around 1985 and I ended up with what I though was an albatross in my room.
I blew out all the output transistors in the original amplifier rockin' it hard and it sat until 2005 when I pulled it out of the basement and began to sort things out, the real estate crash a few years later got it stuffed into a large refrigerator box and stored until this past July when I decided it was time to get it going again. Back in 2005 I replaced the old amp with a Heathkit AA-100 that didn't have a cabinet, the plan with that was to harvest the iron and 7591's but instead it got a re-cap and bias pot mod and grafted into the set, gotta tell ya those alinco magnet 15's on the tube amp really have some sound to them. The tuner was never that great on sensitivity but did sound good, the AM section was never worth a dime and the EM84 tuning eye is weak. The stereo section is tube hybrid, I don't know if this was a leftover at the factory because it's not the one depicted in the service manual set Sams 1109-folder-1 and I can't find the original tag or chassis stamp.

So right now it's working but there are still a number of challenges to sort out, one is the color killer wants to cut the bandpass amp off intermittently, the horizontal osc starts off very high then comes down with heat and the color is still "shallow" meaning it goes away on areas of the scene with low chroma saturation regardless of luma level. At some point in the near future I will photobomb my imgur page with the internals and various other pics of the set, I did do some damage to the finish of one of the sliding doors that turned it a milky white, I know nothing of wood finishes and will post this damage later on.

Mohawk makes a blush eliminator (lacquer thinner and lacquer retarder) in an aerosol can that is intended to fix white blush in recently dried finishes that were sprayed in high humidity (which causes the white blush). I have had luck removing white blush in vintage finishes, hiding scratches, and rejuvenating tired original finishes by orienting the cabinet such that the surface to be treated faces up and is level (otherwise the toner lacquer runs and you get dark runs) and spraying enough to temporarily make that finish liquid. It'll slowly re-dry and be fine.

Progress update. Had a weird and uncommon failure in the 3.58 osc section, the xtal tuning coil literally shorted out. The little dab of wax used to hold the wires across the coil form dissolved the enamel and shorted the windings killing the color and giving me a good week of headaches chasing this one down. At first it was lost color sync then a fade to gray, it acted like the color killer was coming on so that's where I focused until I looked at pin-7 of the 6HS5 and found chroma and the osc, when I bumped the tuning coil the color flashed and that's when I looked closer and found the wax flaking with some green enamel missing.
My fix was using some fine wire from a small audio transformer and winding a new coil, once I had it on frequency it was dabbed with a touch of Testors model adhesive. Not a common repair for sure but my odds of finding another coil is around zero.

So more progress has been made. Ditched the 12AT7 based video input amplifier in favor of an LM1252 video op-amp and basically rebuilt the entire interface board. It still retains the LM1881 sync separator as this has been a real asset when dealing with non timebase corrected videotape sources as I get no flag waving or skew induced distortions. The amplifier has an overall gain of 5 at 75 ohms and this is then padded using a pot which then feeds the pentode grid of the 6MU8 1st video amplifier. Below are a few images of the amplifier and actual raw playback from a tape I made the spring of 1985 using a Sony VO-2600 I bought from a surplus store for $20.00, sorry for the rather poor capture quality. Every time I try to use the Pro camera mode it seems to make things worse and no matter how I try it is never quite right.

Video Interface board: https://imgur.com/T1S6xpU

Tape Starting Point: https://imgur.com/hco1PnH

Actual Screen Capture: https://imgur.com/dUCnGtM

Sony VO-2860 In Action: https://imgur.com/stVHm2b

You mean LT1252.
https://www.analog.com/media/en/technical-documentation/data-sheets/lt1252.pdf
Yep, I would have gone the solid state route also. BUT, it depends on what type of power supply you have available.
Another video chip that's cool is the AD828 from Analog Devices:
https://www.analog.com/media/en/technical-documentation/data-sheets/AD828.pdf
It has high output drive capability and flexible power requirements.
Some time ago, Motorola had an application note called "the last 10 percent" which discussed the issue of "flag waving."
The problem is that the horizontal AFC can't follow the pulses as the signal goes thru vertical sync which are broader than horizontal pulses,