https://chicago.craigslist.org/chc/atq/d/old-admiral-tv/6300445685.html

The case looks nice. I don't know much about this stuff.

Thoughts?

Looks well-worth $60 to me...even has the original back! Restored they're pretty good performers.

It's a 1949 model 12X12 and well worth the price.

It has a 20Y1 chassis with a 12LP4 CRT. Seems to be less common than the earlier 10" version. Nice to have the metal back but the control door is missing and they are hard to find. Mine is missing too.

Here's what it would look like: https://www.pinterest.com/pin/457537643370097998/

NEVER have seen a working model of these.

NEVER have seen a working model of these.

I had one. CRT was almost dead so I had to turn the lights off to watch. Mine did have a good door though. Sold it to Dave (Dieseljeep) a few years back...I sorta miss that TV.

NEVER have seen a working model of these.

A few years ago, I did a slow variac power-up of mine, which still has most of its original parts, and it worked ok.

http://www.videokarma.org/attachment.php?attachmentid=165031&d=1254636306

Gotta give it a full recap job, one of these years. :D

jr

I saw that on CL too!:D I want it as well, but I'm not going to get it. Not interested in goin through Chicago for it. NOPE!


Shouldn't be hard to restore. I restored my 20X122 in exactly 1 week. Works great and has a great pic.

Wonder WHAT was the deal on the funny-shaped CRT ?!?

Wonder WHAT was the deal on the funny-shaped CRT ?!?

It's actually a pretty good compromise between the "double D" mask and the "porthole" presentation. For a 12 inch round jug the vertical display size is increased by about 1/4 inch... not much, but I think that it makes for a more pleasing display. Compare to the 12" Philco next to it.

https://farm5.staticflickr.com/4348/37071321861_4150a86c07_z_d.jpg

IMHO, pretty nice.

jr

Welp, I pulled the trigger.

I gotta say, the case is near immaculate. It has like a grand total of 2 small scratches that you can't even see at 5 feet away. The safety glass is plastic, and amazingly that's scratch-free, too. Inside there's a lot of dust, a mix of tubes, what looks like the original crt, no brightener, and all the pots and switches are free. It has the original metal back cover, and even the power cord, which is strangely still supple and intact. Oh, and it has this weird adjustable built-in antenna, and (I think) an adjustable electromagnetic focus ring? O_o

Sadly the crt tests near-dead.

I tried to bring the set alive on a variac and a wattmeter, but it was very quickly apparent that it wasn't having it. So here's the next question: do you think I could get away with just replacing the filter caps and making sure all the tubes are ok, in order to see if the crt will give me something? You know, before I go all the way and recap the whole thing?


Also, jr, I might have to hit you up for pictures of that front door thing, at some point in the future. :3

Welp, I pulled the trigger.

I gotta say, the case is near immaculate. It has like a grand total of 2 small scratches that you can't even see at 5 feet away. The safety glass is plastic, and amazingly that's scratch-free, too. Inside there's a lot of dust, a mix of tubes, what looks like the original crt, no brightener, and all the pots and switches are free. It has the original metal back cover, and even the power cord, which is strangely still supple and intact. Oh, and it has this weird adjustable built-in antenna, and (I think) an adjustable electromagnetic focus ring? O_o

Sadly the crt tests near-dead.

I tried to bring the set alive on a variac and a wattmeter, but it was very quickly apparent that it wasn't having it. So here's the next question: do you think I could get away with just replacing the filter caps and making sure all the tubes are ok, in order to see if the crt will give me something? You know, before I go all the way and recap the whole thing?


Also, jr, I might have to hit you up for pictures of that front door thing, at some point in the future. :3

Very cool!! Let's see some pictures when you get the chance.

Ya might be able to 3D print that door. It is 2017 after all.

How long did you leave the CRT on? It might wake up and if not it might rejuvenate.

(I think) an adjustable electromagnetic focus ring?Sounds like an ion trap magnet, if it's an adjustable circular gizmo around the CRT neck. You can read about that and many other wonderful details in the Rider and Sams service manuals available at the ETF archive (scroll down to 20Y1):

http://www.earlytelevision.org/tv_schematic_diagrams_admiral.html

do you think I could get away with just replacing the filter caps and making sure all the tubes are ok, in order to see if the crt will give me something? You know, before I go all the way and recap the whole thing?Sure, that's one approach. If your CRT is truly a dud, you still might not see anything, but at least you could measure key voltages and compare to the service manual values, and discover other things depending on what test equipment you have.

Also, as mrjukebox160 notes, some CRTs that look dead at first will "wake up" and show higher emission if you leave them on the tester for a while.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

Some comments.

1. The focus coil can be tilted by moving a lever arm to position the trace... that is the odd arm sticking out of the back of the set.

2. You could try a power-up with the rectifier (5U4) removed, to see if the excessive power draw is caused by the filter caps...you should be able to light up all of the (good) tube heaters, without drawing excessive wattage.

3. Sure, I should be able to get halfway decent close-ups of the door with this iPad.

4. For sure, try an extended "wake up" of the jug.

jr

oops! double post...sorry!

Ya might be able to 3D print that door. It is 2017 after all.

My thoughts exactly!

How long did you leave the CRT on? It might wake up and if not it might rejuvenate.

Eh... about 10 minutes. I don't think I'm gonna attempt a rejuv unless I'm 100% sure it's not going to give me anything at all. I'll try it on the tester again, though.

Sounds like an ion trap magnet

Nope! It's exactly what I thought it was: electromagnetic focus coil. It sez so in the Sams. It does have a trap magnet too...

You could try a power-up with the rectifier (5U4) removed, to see if the excessive power draw is caused by the filter caps...you should be able to light up all of the (good) tube heaters, without drawing excessive wattage.

I might do that!

Also, I pulled all the tubes and tested them, of the 19 tubes, 8 or so are bad in one way or another. I think I have replacements, I'll have to check.

Leave the tube on the tester for ~1 hour check back every 15 minutes. Wake up can be very slow.

... (I think) an adjustable electromagnetic focus ring?...

The focus coil is adjustable so you can center the picture.

Agree about letting the CRT cook for an hour or more. You could try elevating the filament voltage to around 7 while it's cooking too.

Sorry the pics suck bc cell phone. There's a splotch of tar on the front plate - petrified tape residue from another era. An auction sticker on the side in photo #2 gives away a tidbit of this piece's history. Though the seller says he got it from a friend, and had it as a display piece until he moved to a smaller dump.

I took the chassis out and evicted most of the dust bunnies. Inside, it seems only to be missing a single tube shield thingy. Haven't catalogued which tubes I need yet, I only know that I need lots. It's kinda hard looking underneath the chassis with a 100-pound tube weighing it down, but all looks original under there.

Any tips for removing the crt safely?

I don't think there's any waking it up, btw. Let it cook for an hour, still tests around "1." The scale is kind of ambiguous, but 0 to 2 is "Bad," so...

Some testers good/bad indication is not always accurate. My B&K 466 will score some monochrome tubes middle of the bad scale when they still can produce a decent picture in a room with moderate lighting....Same tester will score color tubes that are dimmer in the low good range. It is always good to get to know your tester before using it to make decisions.

It may make a very decent picture with a brightener.

Haven't catalogued which tubes I need yet, I only know that I need lots. ...

Tubes are usually not the main source of trouble in antique TV sets. What you should replace are all the wax paper capacitors and the electrolytic caps.

I've worked on a number of similar Admiral chassis. If the CRT is firmly attached, it's possible to leave it mounted and carefully tip the chassis on it's side to work on it. You may need to place a folder over towel or similar padding to help support and cushion the CRT

Here's where I'm at: I changed the 3 filter caps, and it powers on without throwing a hissy fit, taking only 50 out of the theoretical 200 watts. The main transformer buzzes a little bit still. I'm not getting HV. I replaced 6SN7 (AF amp/sync clipper) and 12AU7 (sync amp/sync sep), which were bad. The only other bad ones (still in there) are audio out, damper, RF amp, and 1st video IF. The 2 tubes in the HV cage are both good, and filaments light up.

I just want to see if I can get a beam out of the crt. I really don't want to recap the whole thing only to find I need a flyback or something. Not to mention the crt.

Ideas?

http://www.earlytelevision.org/pdf/Admiral_20X1_Sams_100-1.pdf

You're very likely going yo have to do some recapping to get a raster. At least the horizontal oscillator and output circuit. Also this set uses a stacked B+ power supply design so the sound output tube needs to be biased correctly. Also make sure the speaker is pullged in as it's field coil doubles as a filter choke for the power supply.

I wouldn't worry about the flyback. I've never encountered a bad one. Also I[m local to you and have spare parts.

Here's where I'm at: I changed the 3 filter caps, and it powers on without throwing a hissy fit, taking only 50 out of the theoretical 200 watts. The main transformer buzzes a little bit still. I'm not getting HV. I replaced 6SN7 (AF amp/sync clipper) and 12AU7 (sync amp/sync sep), which were bad. The only other bad ones (still in there) are audio out, damper, RF amp, and 1st video IF. The 2 tubes in the HV cage are both good, and filaments light up.

I just want to see if I can get a beam out of the crt. I really don't want to recap the whole thing only to find I need a flyback or something. Not to mention the crt.

Ideas?

http://www.earlytelevision.org/pdf/Admiral_20X1_Sams_100-1.pdf
Did you have the speaker plugged in? It completes the B+ circuit!
It would seem that way, as the power consumption is only 50 watts.

Also if the damper tube is bad there is no way in hell you'll get HV out of it.

Expect to replace some lytics, the paper caps in the horizontal section and any paper caps on the B+ boost line that the flyback supplies before HV materializes.

Also make sure the speaker is pullged in as it's field coil doubles as a filter choke for the power supply.
Did you have the speaker plugged in? It completes the B+ circuit!

lol I thought the speaker was wired strangely!

Also if the damper tube is bad there is no way in hell you'll get HV out of it.

Expect to replace some lytics, the paper caps in the horizontal section and any paper caps on the B+ boost line that the flyback supplies before HV materializes.

Thanks guys, I replaced the damper tube, and plugged in the speaker. Got a raster! It actually looks... not too bad given that it's all original (minus the filter caps). It lost it for a minute though, not really a big surprise, but it came back. I hadn't changed the damper tube because I thought I didn't have one! My dead-project RCA Victor tv DID have one though. Also the tube is surprisingly bright for testing 'bad.' Even in my brightly lit room, you could probably watch a show no problem.

brb recapping.

Cool! You're well on your way to having a fully working set :) Funny how a seemingly dead CT can produce a decent image.

I recapped about 80% of it, I ran out of caps I needed, and I still need one tube, a 6BC5. I put a test pattern signal into it, and it honestly looked like crap. Now I wait for parts to come in.

Hmm. I don't see a 6BC5 in the schematic. I'm thinking it's in the tuner but that shows a 6AG5. Perhaps is a production run change ? If it is in the tuner and is bad, for sure it would result in a crappy picture.

Hmm. I don't see a 6BC5 in the schematic. I'm thinking it's in the tuner but that shows a 6AG5.

*scratches head* Dammit! And I already ordered a tube for it - the wrong tube, it is supposed to be a 6AG5. The vertical osc/amp tube was also wrong, a 12BH7 instead of 12AU7. According to my tube book, they're close approximations of each other, but meh. I'll just order another tube. I did put a 12AU7 in it, it didn't seem to make much difference.

Tube substitution manuals: For the repair man who's tube caddy ain't big enough for two similar types with different numbers... :D

If the other type seems to work well in the stage then it may as well stay, but if it don't going for the original number is the wise choice.

Truth be known, I store my tubes in tube caddies. Today,you can have a caddy for radio, another for audio, another for B/W sets etc. :D

That way, they ain't so heavy...

Truth be known, I store my tubes in tube caddies. Today,you can have a caddy for radio, another for audio, another for B/W sets etc. :D

That way, they ain't so heavy...

I sort of do the same thing....The stuff I've had the longest are in caddies sorted by number and tested. After that is is an unsorted mix of boxed NOS, and semi-sorted loose pulls (some stored in boxes after the caddys filled)...The pulls are sorted by type (HV diodes sweep power tubes, 7 pin, 9 pin octal/loctal signal, fat pin) A caddy FILLED with un-boxed loose pulls can get heavy fast. :D

*scratches head* Dammit! And I already ordered a tube for it - the wrong tube, it is supposed to be a 6AG5. The vertical osc/amp tube was also wrong, a 12BH7 instead of 12AU7. According to my tube book, they're close approximations of each other, but meh. I'll just order another tube. I did put a 12AU7 in it, it didn't seem to make much difference.

A 6BC5 is the newer generation 6AG5. I seldom bought 6AG5's, always 6BC5's.
Way back then, I would try different variations of similar tubes, 12BH7 vs 12AU7 etc, to avoid having to troubleshoot the circuit.
That was in jobs where the set owner didn't want to spend too much money on an old set. :scratch2:

I sort of do the same thing....The stuff I've had the longest are in caddies sorted by number and tested. After that is is an unsorted mix of boxed NOS, and semi-sorted loose pulls (some stored in boxes after the caddys filled)...The pulls are sorted by type (HV diodes sweep power tubes, 7 pin, 9 pin octal/loctal signal, fat pin) A caddy FILLED with un-boxed loose pulls can get heavy fast. :D

Many of us could probably cull our loose/unboxed tube collection by:

1. testing all the HV rectifiers 1B3-1X2-1V2-3A3 etc weeds out the open filaments at least. Id hate to stick a bad one in a working set.

2. testing all the damper tubes for gas-shorts again where fails are obvious on a simple tester

3. Testing 5U4's and sweep tubes in a working set. emission testers miss often the bad ones

4. Run a quick shorts-gas test on all the common triodes and pentodes 6CG7, 12AU7, 6SN7, 6CB6....

Ok, so. I recapped most of this set, but the picture didn't want to be right. So I ordered the rest of the caps, but then capacitorworld decided to screw up my order again, so I had to wait a while. I just got them today (from digikey) and put them in, but the picture is still crap. All the tubes test good, except the audio output (tested questionable), but the audio comes through clear (though with some buzz [a lot of buzz if the audio is silent]).

I've been fiddling with the adjustments. I noticed that the horizontal lock in range and horizontal drive trimmer caps were all the way screwed in, and the horizontal linearity coil thingy was very much screwed out. My main problem is with horizontal (although it looks like vertical has an issue too), as it seems the picture is overlapping itself several times horizontally. I'm a total noob at this, but judging by sound, it seems like the horizontal lock adjustment on the front speeds up or slows down the horizontal... um... 'drive'? But anyway, if I turn it up, the picture overlaps itself more, and down less. Unfortunately, it seems that the H lock in range is best set as far in as it can be. The H drive seems not to do much at all, but the picture is a bit clearer at just slightly less than all the way tight.

The other adjustments seem not to affect it much, which makes sense to me. The only thing I noticed while recapping is that one cap seems to have been replaced with a bumblebee. It was in a totally different place than in the Sams photo, and the leads of the snipped-out old one are still there. The stripes are discolored and I'm colorblind anyway, but my thingy measures it at .02 so I put a .022, but the diagram calls for .01. It's C32 for anyone with the Sams. It just goes to ground from a sort of... 'rail' that comes off of one side of the brightness pot, it goes to lots of things including a grid on the video amp and the audio output and all over the place. Actually now that I really look at it, it seems to have a lot to do with the horizontal stuff. Hmm.

The pic below is supposed to be an indian head test pattern.

Ideas?

Looks like the horizontal frequency is too low... there is a slug adjustment on the back of the chassis for horizontal frequency (it is protected by a metal bumper) turn that and observe the effect on the multiple overlapping images.

jr

Hi,
I finished up a recap on an Admiral 20X1 chassis a few weeks ago. I was having trouble with horizontal AFC , just like your picture shows. I found the issue in my case, was the horizontal stabilizer coils' adjustment. It is on the underside of the chassis. I had to back (turn) the slug all the way out, to the end of its' travel. This adjustment is on the opposite side of the horizontal frequency control slug.
Make sure you follow the set up procedure in the Sams for the horizontal oscillator adjustments.
I posted a picture with an arrow pointing to the slug adjustment.
Ed

Thanks guys. I had played with the H frequency before and it did nothing. I went back and unscrewed it nearly all the way, and the picture fell right into place. And I didn't even realize there was a thingy under the chassis. One little problem though...

I'll be following the Sam's instructions for an o-scope based alignment. But idk if that'll fix this. And before you go and mention the picture alignment device, it's already maxed out. Plus there's a clean straight end to the picture.

EDIT: apparently my input device is messed up. fml

OK. Update time.

I got a new thingy. I followed the whole big horizontal adjustment guide on sams to a tee. The picture is not bad, but it's not really any better than before I did the whole procedure. The only noteworthy thing about the procedure was that I was unable to get the picture to slowly scroll horizontally, in the one step that asked for that. The picture either flies by all skewed, or the closest I got was the picture far to one side with a bit of a ghost image next to it. Also, I think it asked to see the retrace as a bar on the side, and I couldn't find that either.

It's hard to tell from the photos, but the picture is pretty blurry. I could be mistaken, but it seems like it gets a bit worse as the set warms up. The focus is turned all the way up, and it does get worse if I turn it down. Maybe one of the resistors associated with the focus is bad? There was a capacitor I mentioned earlier on that was double value on the same circuit, I replaced it with the specified one, and it did jack.

There's also a shadow of everything, if you look closely, especially noticeable in the darker image.

Turning the brightness down improves the clarity of the image, but even with the lights off in the room, the image would be too dark (and have too poor a contrast) at a level of brightness that produces a clear enough image. On the other hand, with the brightness all the way up, though the image is blurry, the screen is pretty damn bright. So... the crt is good, I guess?

The thought occurred to me at one point that the ion trap might be out of whack. Before doing anything to this set, the FIRST thing I did was mark where it was, so that's where it stayed. But I decided to mess with it, and while I don't know ANYTHING about adjusting an ion trap, the picture is at its brightest where it was rotationally, but I found that backing it up about 1/4" made it even brighter. Is that... ok? The photo below shows where I moved it to.

Also, the horizontal linearity slug doesn't seem to do much at all. All the way in or out, it has VERY little effect. And no matter what I do, the left side of the image is a bit stretched out.

With Ion traps you adjust rotation then fore and aft for max brightness...If neck shadows or centering issues occur occur try to fix it with positional adjustment of the focus coil first and only try to fix them with the ion trap as a last resort.

Double magnet traps like yours only have one 'front' side (be sure not to reverse it). But single magnet traps can use either side as front and sometimes work best if you swap front and back (the rotational sweet spot will shift 180 degrees when you flip it). I mention single magnet as they are more common and if you own enough sets you will run into them eventually.

...So what you're saying is... I did it right without even knowing what I was doing? Score!

Also I have no way of knowing which direction the magnet is supposed to be, other than the way that I found it. It has no arrow.

"Maybe one of the resistors associated with the focus is bad? "

The resistors would be the first thing that I would check. Are you getting too much or not enough current to the focus coil?

jr

...So what you're saying is... I did it right without even knowing what I was doing? Score!

Also I have no way of knowing which direction the magnet is supposed to be, other than the way that I found it. It has no arrow.

Black to the base - it's on backwards. Also the linearity and width slugs have a very subtle effect and are meant for really fine tuning the picture.

MadMan,
After you reverse the ion trap and reset it, you may find an improvement in the focus. Otherwise everything looks good :thmbsp:. Some of the horizontal linearity issues and slight phase shift you mention seem to be inherently common with these Admiral sets. The last three Admiral sets I repaired had some of the same issues.
I just got an Admiral 12X12 this past weekend, won't get to it till next year.
Did your set come with a metal rear cover and metal underside shield ?
The rear cover that came with mine looks it may fit more than one model.
Ed

Did your set come with a metal rear cover and metal underside shield ?
The rear cover that came with mine looks it may fit more than one model.
Ed

Yup, I has cover ^_^ but ty.

Black to the base - it's on backwards.

Ah. Thanks. Well. It was like that, so not my fault. Actually now it makes sense - blue for electrons, black for the base.

I flipped it around and it seems to have made no difference in the clarity of the image. Perhaps I should readjust horizontal. However, I had to shove it all the way forward on the neck, touching the focus coil. Which I might move it back a bit so the focus can be adjusted, but hey on the plus side, the focus coil gets to be a lot more straight now.

Idk, how awful would it be to put it on backwards? I'm concerned that in the future if the focus coil adjuster gets bumped, it'll snap the crt neck, what with the magnet butting up against the coil.

Can always loosen it to the point where it won't spin or move easily, but will move with a little bit of force.

"Turning the brightness down improves the clarity of the image, but even with the lights off in the room, the image would be too dark (and have too poor a contrast) at a level of brightness that produces a clear enough image. On the other hand, with the brightness all the way up, though the image is blurry, the screen is pretty damn bright. So... the crt is good, I guess?"

Pretty good indication of a weak CRT... yes you can turn up the grid drive and get a fairly bright image but not good focus, as the "sweet spot" (center) of the cathode is depleted... when you turn up the drive, you are drawing more electrons from off center areas, this is not conducive to good focus. Hopefully, the cathode will improve as you run it longer, or perhaps try to re-activate by running the heater at increased voltage (like 7 to 8 volts) for a few hours.

jr

Pretty good indication of a weak CRT...

Well... big surprise, right? I had it running the other day and it seemed better, but like I said, it really seems to get worse as the set warms up, but I'm not 100% sure about that. I'm still going to inspect the focus circuit anyway. Plus I still got that slight shadow, but maybe that's not related.

Ok. So.

I was thinking (yeah I know, that's my problem right there) if I could increase the voltage going through the focus coil it might focus the picture better. To do this, I used my decade box to put a resistor across the focus pot, and it worked. The picture was razor sharp. Though, come to think of it, I'm not entirely sure if the resistance I added increased or decreased the voltage through the coil. :/

I only had it on there for a minute max, but when I removed it, the picture was blurry as hell. I let the set cool off and it seems to be almost back to its normal level of blurriness.

Did I break something?

Things to consider: Current through the coil often matters more than voltage. Most decade boxes use half watt resistors. The average focus coil can handle most or all the B+ current through them so the focus pot often is/needs to be a 10-25 watt resistor to handle the power...If you put a half watt resistor big enough to significantly effect the control in parallel with it, then odds are that resistor is going to see several times it's rating and burn open......
Some time ago I found a sencore 'Big 20' which is a decade box made with 20 watt resistors...It is situations like this and power supply work where that box really shines.

Check your decade box is in spec on the setting(s) you used, and if the setting you were using is out of tolerance/open replace the one in the box, and get a 20W unit the same resistance to use in the TV.

Check your decade box is in spec on the setting(s) you used, and if the setting you were using is out of tolerance/open replace the one in the box, and get a 20W unit the same resistance to use in the TV.

lol my decade box uses wire wound resistors. idk what wattage but I'm certain they can handle it. Besides, does care about the box, I'm worried about my tv.

Just to nit pick. It's voltage across the coil and current through the coil. Anyway. you definitely do not want to burn out that focus coil. If B+ in the set is close to what the service info specifies, I'd look elsewhere for a solution.

For instance, the entire focus coil/yoke assembly can move back and forth on the chassis. There are two large screws down at the base that hold it to the chassis and there are slots in the support. It was designed so that you can loosen those crews and move it around. It might not be in the "sweet spot" for this particular CRT.

Alright I found the focus problem. I spent a good amount of time today going through all the voltage checks - and many of them (~25%) are WAY out of whack. So I sat back and did some thinking, and it occurred to me that I should just do what I originally wanted to do - investigate the focus circuit.

I disconnected the focus pot and big resistor that comes off of it. The resistor is in spec, but I found the pot was open from one end to the other. I took the pot off the chassis, and cracked it open and immediately could smell it was fried. It's still stinking up my room, my god, it's so pungent. If you look at the pic, you can actually see the bit of wire that broke and is now rubbing on the... turn-y thingy.

So there's that. Apparently, my adding a resistor across the pot was actually completing a previously open circuit, and that's why the focus would work properly then.

New thingy is on its way from fleabay already.

This just leaves me with the H linearity problem and hopefully this new pot will bring all the voltages in line, because some of them are really far off.

On wire wound pots (cough rheostats cough) you can often bridge the open and get the pot usable again.

In that rheostats case, you may need to add series resistance (given a lot of turns look bad) and reverse the ends of the pot so the wiper/rotor does not rest in the bad zone when focus is adjusted. Necessity (or cheapness and poor parts availability) is the mother of invention (but does it have Zappa too?).

On wire wound pots (cough rheostats cough) you can often bridge the open and get the pot usable again.

My first thought as well, but it's pretty screwed up. You can see a large section of turns aren't damaged, but the ring they're on is wrinkled inwards.

2 years later update!

This thing's been sitting on its side in the middle of my bedroom for the past 2 years. I've been struggling with this stupid horizontal linearity problem. The left side of the picture was stretched out, and no matter what I did, it just didn't work out. But today I decided to take a fresh look at it, I tried a bunch of things, poked a bunch of stuff, and it was a little frustrating, but then something clicked. I'd been focusing on the linearity area. Mind you, I've never repaired or adjusted a tv like this before. But I decided to start messing with other stuff related to horizontal.

Wouldn't you know it, the horizontal drive trimmer was the culprit this whole time. It was about 99% tight, and if I loosened it, it worsened the stretching on the left side. So I figured that if I add a capacitor in parallel, it should either make it worse or better, either way, that was the culprit. I dug up a 22pF disc cap, put it on, and it happened to be just about right. I could now adjust the H drive to get the picture almost 100% linear.

It's still not 100%, but you know, 99% is pretty good for a 70 year old tv. And I'm quite proud of myself. :3

I'm imagining a 1kv ceramic cap would be acceptable for that area? I was considering replacing the actual trimmer, but it still works, I think maybe it's simply drifted to a lower capacity? Idk. Also, there's a bit of a neck shadow in the lower right corner, but I've given up on that. Doesn't bother me much, anyhow. You can see the stretched out test pattern here. (http://videokarma.org/showpost.php?p=3191282&postcount=41)

Now onto another project, I'd like to add RCA inputs. Any good threads on the topic?

Nice!

Looks good. The drive should be in the grid circuit of the output so 1KV will work and give you a large safety margin.

Good sleuthing! There was a run of RCAs of about that same vintage afflicted with bad horiz linearity that Nobody was able to fix, and finally had to pass it off as the 'nature of the beast'. Gotta wonder now if it coulda been the horiz drive trimmer all along.

That looks very, very good. Thanks for the update.

Ok, so...

*sigh*

Since it's been over a year since I've last run actual video through this thing, I seem to have forgotten its other problem. If the video being displayed is too dark (seemingly an average of the whole picture), the image becomes bright and washed out, and the retrace lines show up. With the test pattern, the contrast knob is right about in the middle, and it displays perfectly. With any other image, yeah pretty much ANY other image, if it's not mostly brightly colored or white, this happens. The darker the image, the worse it gets. With any letterbox video (because of the black bars) it's terrible, and no amount of contrast adjustment makes it better.

Imagine you're watching a tv show. With every scene change, the contrast of the picture gets changed.

I feel I should also mention that depending on the video, again, the darker it is, the more buzz that's audible in the audio. This problem isn't really an issue when you're watching the tv - it's not noticeable. But I thought I should mention it as it might be related.

Thoughts?

The set probably lacks DC restoration in the video...Many sets back then were like that and those that didn't grow up with it think it is a defect.
It is possible to add DC restoration and there are articles on it in period TV repair magazines.

There probably is a retrace line suppression circuit in that (if not adding one ain't hard) should be from the vertical output to the video...play with the RC time constraints and see if you can improve things.

The set probably lacks DC restoration in the video...Many sets back then were like that and those that didn't grow up with it think it is a defect.
It is possible to add DC restoration and there are articles on it in period TV repair magazines.

There probably is a retrace line suppression circuit in that (if not adding one ain't hard) should be from the vertical output to the video...play with the RC time constraints and see if you can improve things.

I understood about half of that. What are RC time constraints? What does DC restoration do, exactly? Is that only for hiding the retrace? Because I could care less about the retrace. The contrast is not stable, that's the real problem.

RC = Resistor Capacitor there should be such a circuit coupling the vertical to the video to eliminate retrace.

DC restoration has nothing to do with retrace. When video amplifiers are AC coupled (which is the case most sets) the DC level of the video at the detector is normally lost...It manifests it's self in many ways such a scene with one large black and one large white section side by side smearing when fine detail looks good, the brightness immediately after a scene change either being lower or higher than average and sinking or rising despite image content being fairly constant...Things like that.
Some RCAs, Dumonts, etc dedicated a diode in the video output to the task of restoring DC level to the video. I forget the exact electrical description of their operation. They became standard with color TV, but in the monochrome era they usually were only in the more expensive sets.

if the retrace lines are not there with brightness turned down to a dim picture its a weak crt

if the retrace lines are not there with brightness turned down to a dim picture its a weak crt

Well, it's not the strongest crt. And come to think of it, I have had the brightness all the way up. At max, it's very watchable in a bright room. Of course, I understand it wasn't necessarily meant to be watched in a bright room. I tried lowering it, and it does help greatly with the retrace, they still show up with a very dark video image being fed through. I think the CRT is slightly weak, but I have other problems.

So here's what I have so far. I'm not seeing any problems underneath. There is one big resistor (1M) that seems to have drifted a little high, but that's about it. Of course, I haven't checked everything, just what I've seen so far. It's R38 and it goes from the grid of the sound IF amp tube to ground. The grid is also coupled to the video output via a 2pf capacitor. I was looking in that area, because of the buzz in the audio.

If you feed in a white image, it increases the buzz in the audio. The same is true if you turn up the contrast. On a test pattern, if you turn up the contrast past 80% or so, the picture smears. But as most video images are a lot less white (on average) the picture will not smear.

I did a little watching of old tv commercials, etc, all stuff that was 4:3 (so no black bars), and it was reasonably watchable. Retrace was rarely on screen, and the huge swings in contrast between bright and dark images wasn't really an issue because most video from back in those days was brightly lit stage recordings. So perhaps it wasn't an issue in 1948, but given that we are living in the next millennium...

The diagram shows a direct connection from one side of the primary winding of the transformer that feeds the vertical of the yoke, that goes to a grid in the CRT. Would that be the retrace suppression? I'd imagine when the input goes positive, it would blank the screen. Or perhaps that's the old fashioned way of doing it, and not terribly effective.

Still, I'm more interested in this DC restoration. If I can rig it to keep the contrast constant, the retrace lines will not be a problem at all. Because if you have a constant picture on the screen, adjusting contrast and brightness to hide the retrace is easy. I'm looking up old threads on the topic, but if someone would care to chime in, that would be great.

“The diagram shows a direct connection from one side of the primary winding of the transformer that feeds the vertical of the yoke, that goes to a grid in the CRT. Would that be the retrace suppression? ”

The line between pin 10 (grid2/anode1) of the crt and the red wire of the vertical output transformer merely supplies boosted B+ from the damper to both points. As far as I can tell, the tv does not have a retrace blanking circuit.

jr

The line between pin 10 (grid2/anode1) of the crt and the red wire of the vertical output transformer merely supplies boosted B+ from the damper to both points. As far as I can tell, the tv does not have a retrace blanking circuit.

jr
Yeah, that's starting to make sense.

I really couldn't find a whole lot about DC restoration... other than unhelpful theoreticals, and this. (https://antiqueradios.com/forums/viewtopic.php?f=3&t=194179)

I have attached the video output portion of the schematic. Can someone tell me if this is grid or cathode driven video?

I *think* it's cathode drive. But it seems I don't know nearly enough about the actual theory of operation to know what I'm doing. I tried putting a silicon diode and 200k resistor in series with the cathode wire, basically, and it made no difference. The resistor alone just made the image very soft and blurry. If it was cathode drive, wouldn't it dim the image?? I suppose maybe the diode I have leaks too much reverse current at that voltage? Then I tried putting the diode across R35, and it arced rather loudly (oops), tried it the other way around and it made no difference at all. I did also try adding a ~4uf capacitor to ground, also no difference.

I'd really appreciate a suggestion.

Definitely cathode drive, the video signal is connected to the cathde (pin 11) of the CRT. The grid (pin 2) only gets a variable DC voltage to set brightness. I looked briefly for a DC restore circuit that can be used with cathode drive video and have not found one yet. Will look some more tomorrow.

jr

Thanks jr. I had hooked the O-scope up to the cathode and saw video there, I just wasn't sure because I don't know enough of the theory.

I suppose the issue I'm experiencing is likely not even a AC/DC problem. Because the cathode is negative, and more negative voltage would be more white on the screen. So what I'm having is the zero point not being clamped to 0v, but fluctuating. (Right?)

Now that I think about it, then, a diode would be entirely useless. I probably need some much more complicated circuit. Unless I go before the video amp and correct the issue there, or further back. Hmm...

This chassis does not have a retrace suppression circuit but it can be added easily as described in Riders Receiver Troubles and Cures vol 1 page 1.

https://www.earlytelevision.org/rider_cures.html

some years ago, I posted a resto of an RCA 6T75 chassis with bad horizontal linearity much as youve shown. Now im excited to dig back in and see if I can improve it with the drive trimmer! thanks for the motivation. incidentally that set has shadowing similar to yours, and ive never solved it.

im on my phone and couldnt get a great look at the video section of your schematic...but rhe set does appear to lack DC restoration as has been said.

skmewhere I have a 1950 breitman service book with dozens of late 40s schematics...Ill also look for a similar cathode drive circuit with a dc restoration circuit.

can you pass along your full schematic? or at least pass me the chassis number? Im a little late to the party...

thr RCA has a phono input with a switch that blanks the video...i repurposed thr switch to also cut over to an composite video input, which in thr RCA is relatively painless to add.

BTW, i find a strange array of sets Have/dont have dc restoration. by 1950 even Muntz sets sported DC restoration at thr lowest possible price point. honestly, i suspect that with low contrast "live" images of the late 40s, youd never notice the difference. With high contrast content now, the difference is fairly bothersome.

Here's the schematic. (http://bans.rawcg.net/temp/Admiral_20X1_wiring.jpg)

I'm glad I might've actually helped someone else with their problems, hopefully. I suppose the thing that gave it away on my set was that I messed with the drive trimmer and it made the linearity worse, so I figured I could make it better with more capacitance.

Thanks for your interest in my case. If you ask me, it's very important to keep these old things actually useful. I'm getting the vibe that many here like to restore tv sets to the way they were, and even use them that way, but that way is already long gone. If we want to preserve these pieces of history, I feel like it's paramount that they can actually be USED for some functional, present-day purpose (even if I personally don't plan to watch a whole bunch of tv on this set). You know what I mean?

Let me get down from my soap box here.

Anyhow, um, as for the shadowing, I don't think there is much to do about it. I'm trying to picture it my head, you'd have to move the beam over. Wait, is that even possible? Like, you can bend the beam, but can you just nudge it over? I suppose maybe... a different ion trap? Perhaps if you mess with the deflection outputs... Say, add a resistor and a diode in parallel with each other, but in series with on one side of the horizontal output. That would force the horizontal to favor one side, I think. idk, I'm just spitballing.

I was thinking, for the DC restoration, when the video signal goes higher (negative-er), it could power a transistor base, and that transistor could be used to pull the video drive down closer to zero. It would probably take an immense amount of fine tuning. It would need a specific capacitor to average out the video signal, and it would probably need a diode to prevent it from having a feedback loop (or whatever you'd call it, when the transistor lowers the voltage going into its base and then unlowers it, etc).

My other thought was to bypass the whole video section and use solid state electronics to do the whole job, but that seems like a bit of a cop-out. Not to mention difficult.

Have you tried adjusting the centering control lever? It pivots the focus magnet around the neck. You might also make sure the yoke is pressed up firmly against the bell of the CRT. Also can you make the shadow go away by moving the on trap magnet around?

Don't get discouraged! I don't know what your background with regard to electronics is, but you've made this set look pretty good in my opinion.

Even as a practicing engineer, I look at a lot of 40's schematics and say either 'what the heck is that', or 'how in the world did they come up with THAT!'

So, interestingly enough, the 1950 Breitman manual shows a ton of schematics, more than half of them have DC restoration. (interestingly none of the cathode driven sets seem to have it, but I think thats coincidence) The 1951 Breitman manual shows the next years sets, and only a handful have DC restoration. Even sets from GE lack it. I'm going to say that with content of the era, average video brightness didn't change much, and manufacturers found they could save one tube with minimal impact.

If you're interested, we can talk more about DC restoration either offline (or in the forum). It's not unique to TV. The basic circuit only takes 2 or 3 parts (1 diode, 1 capacitor, 1 resistor). Its used any time that you have to AC couple a signal for amplification or other reasons, but then want to 'restore' the DC information that was stripped off the signal when you AC coupled it.

As you know, the average video voltage is low for an all black screen, and high for an all white screen. The DC information is ALWAYs lost in broadcast reception, and even if it weren't it would be lost in the amplification stages. (and actually for your set, it's reversed since you have cathode drive which reverses the polarities) If you fed your set an all black screen, it would eventually settle in to '50% brightness). If you then immediately fed it an all white image, it would flash white then fade to 50% brightness again once the DC image level ceased to pass the amplifier.
TVs use the level of the synch tips as the DC reference level for the picture - however the absolute voltage of the synch tips also changes over time with picture brightness. So, we create a circuit that looks at the 'local' height of the synch tips and recreates the picture information relative to that. the time constant of the circuit allows our reference level to change over time as brightness level changes.

I have no experience picking the time constant required, but we can look at other sets for ideas. What I've attached seems typical.

I came up with the attached schematic. and ran a quick simulation with some video waveforms. I *think* it should work well enough. Though, you'll probably have to tweak the values. The diode can be any low capacitance signal/detector diode. You'd be wise to go with 400V or greater. Play with R5 some - my guess is that small values (or zero) will make dc restoration better but may cut down video bandwidth. larger values will not restore dc as well, but will have less effect on video. This circuit also adds an additional cap into the video chain - it may or may not have an effect on video bandwidth. try it and see. Once you find a place for the circuit, you can play with the values.

I attached a picture of my 1948 RCA 6T45 test pattern, as well as a live image. I dare say that you have a much better picture.

So...hopefully you didn't dig into that circuit too much :D

It should have been obvious, but that circuit will also lose the DC level over time.

Cathode driven DC restoration is indeed a little bit more difficult since the set requries the cathode voltage to be about midway between the video amp plate and GND.

Anyhow, I gave it some more thought. We need a way to clamp the DC level to a reasonable voltage that is stiff. What I came up with uses the same 2 470k resistors to set the cathode bias, but rather than come off the video amp output, the 'top' 470k connects to C40 -- the same place the brightness pot taps off of. Those resistors give you a voltage at approximately half the video amp screen voltage, which is then stiffened by a 5uF (or so) 250V or better electrolytic.

D1 clamps the black level relative to the new 250V point. C2 and R6 set the time constant of the DC restoration (it's set similar to other sets of this era). The comments about R5 still stand - bigger R5 gives worse DC restoration, but might give better video and/or avoid synch problems. Give it s spin and see what works.

I've attached the new schematic.

I attached some simulated waveforms of what you might see at the original cathode and at the cathode with this circuit. The DC restoration isn't perfect, but it should be better than what you have.

I created some simulated composite video with positive synch (like you should have at the output of your video amp). The simulation has a bunch of lines of high brightness followed by a completely black section of video, where there is nothing above the synch pulses.

The original composite video is at top, the DC restored cathode signal in the middle, and the original circuit's cathode at bottom.

I'm not sure the AC coupled composite simulation is entirely accurate...but at least it shows how the set's original video amp causes black to fade to gray, while the new circuit eventually finds the right black level after an abrupt brightness change.

Nothing's perfect, hopefully this is something that others can common on and improve upon. After looking I was unable to find any actual schematics of cathode driven sets with DC restoration.

Wow thanks! That's super helpful!

How does THIS (https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/RMPG06G-E3-53/RMPG06G-E3-53GICT-ND/9600316) diode look? It's low capacitance, 400v, and fast recovery time. But all the capacitance ratings are at like 4v, so idk.

Also, which values do you think I'll have to tweak? All of them lol? And lastly, would wire wound resistors work in a pinch? That's about all I have on hand, if they'll work for testing, I'll order carbon later once I have the values picked.

Ideally youd use a shottky, but the voltages are too high. id get something categorized as an ultrafast diode. stth1r06 is my favorite.
https://www.digikey.com/product-detail/en/stmicroelectronics/STTH1R06RL/497-3243-1-ND/654613

the biggest thing to tweak will be C2. i would think values between .01 and .1uf are reasonable. i thought .022 was a good place to start.

if the brigtness ends up on one end of the dial instead of centered, you can adjust one of the 470ks to tweak thr bias.

if it looks okay, and still synchs etc, youre good to go. if it interferes with synch..try to increase r5 to about 1k.

you could use WW on thr 470ks, but i wouldnt use them in the video path.

no guarantee this will work, but its cheap, and it looks good on paper.

Just one additional thought:
The 12LP4 datasheet for your CRT shows that the Heater Negative with respect to cathode shouldn't exceed 140V.

Without the sams, its not immediately obvious what the plate supply voltage is on the video amp. But, if you implement this, make sure the average heater to cathode voltage doesn't exceed the limit.

dobulee, for the love of god don't take this conversation offline please! I'm working my way through a couple of TV engineering books right now and this discussion was super, super helpful to me. Thanks!

Most of the DC restore circuits are more complicated than this, and a lot of them use the same triode for synch separation and DC restore. It makes some sense, since the triode grid gives diode action when driven positive.

Im interested if the above circuit functions decently or not. Im sure the original set designers (and others here!) are aware of more practical limitations and tradeoffs than I am.

screen shots and/or scope captures would make for further discussion! that little simulation doesnt model the video pentode output impedance or anything...so...mileage may vary!

Just one additional thought:
The 12LP4 datasheet for your CRT shows that the Heater Negative with respect to cathode shouldn't exceed 140V.

Without the sams, its not immediately obvious what the plate supply voltage is on the video amp. But, if you implement this, make sure the average heater to cathode voltage doesn't exceed the limit.

Heater negative is just ground, I believe. So basically cathode to ground, then? Voltage chart says video amp plate voltage is 120vdc, measured to pin 1 of V11, I'm guessing a positive... rail... or whatever. Main voltage supply type thingy. The crt cathode says 115vdc, presumably to ground.

I have ordered some diodes. Will keep you posted.

Alright, so I assembled the circuit as described, and it causes some pretty wild image instability :/

Some tearing near the top always, with image/scene changes the horizontal and vertical stabilities change, sometimes the image jumps halfway down the screen, other times its starts to roll. Contrast control used to affect image stability, but now contrast, brightness, and focus have drastic effects on it. And at all times, no matter what, the image is never perfect. At best it's skewed and jittery, and ripple-y.

That all having been said, I *think* it helps the DC restoration, but it's kind of hard to tell when the image is getting as screwed up as it does.

So I'm thinking. This shouldn't affect anything but the brightness and contrast, yeah? Is there some way of isolating it (more) from the rest of the workings? Or wait. The path to the cathode used to be a capacitor and resistor, so that would mean it's capacitively coupled, but with a limited straight connection. Now it's just capacitive only. Would a resistor over the first cap help?

EDIT: I also tried a 1k resistor for R5, it barely made a difference.

if you put a resistor over the cap, you wont have DC restoration anymore :D the resistive path to common is now through the 2 series 470k resistors.

unfortunately I do not have a cathode-video set to experiment with, however, i suspect the tearing problems are due to the circuit interfering with the synch separation, which also comes off the video amp in your set.

anyhow, thats the basic idea:
a diode to clamp the black level
capacitively isolate the CRT grid from the DC level of the video amp
set the DC cathode level with a resistor divider

the details are the complicated part!

go even to 10k at r5. without a similar set, I cant do much other than consult :/ do you by chance have a scope to post some waveforms? as a last resort, i can try to simulate your entire video amp circuit, but i wouldnt have a lot of faith in the tube models up in the Mhz range, if the models even exist.

for what its worth, the 48 RCA 6t45 chassis has dc restoration, and even it doesnt work thr greatest. I took some captures of thr cathode waveforms with all black and all white screens -- i will post them over in the 6t75 thread. But the front porch "black" level on the CRT grid drifts by about 10 volts from "all black" to "all white", causing all black to look gray. That set uses a positively biased triode grid to get diode action from grid current - and it probably doesnt make for the "tightest" clamping.

if anybody else has ideas, id love to discuss. seems like an interesting little project.

Alright I experimented a bit today. First thing I tried was to change R5 to 10k. It made a big improvement in stability. yay! In fact, about 99% of the problems could be adjusted out, and did not come back with changing images. Now, I made a set of test images and use them in a slideshow for testing. I have a regular test pattern, all-white, all-black, then 4 sets of half black on top, bottom, right and left. They don't really approximate rapid scene and lighting changes, but they work well enough for basics.

First thing I noticed was that on the all-black and top-half-is-black* images, the black level starts out at about dark gray, then fades to medium gray over the course of 1-2 seconds. However this happens in reverse when going from all-black to side-half-is-black, where the black area starts (darker than it is with all-black) dark gray and darkens down to a good black. Which, I'm guessing, is what you intended to happen. Why it happens in reverse on all black is beyond me.

*top-half-is-black improved with later modifications.

Then I tried lowering C3. This brought back some of the stability problems and generally made it worse. I then raised it to .2uf and it made things better. Better stability and better evenness of black areas, but not really better black levels. All-black was still the same medium gray. It also seemed to help a bit with retrace lines. I added .1uf more to it, which improved it only a tiny bit more, it seems it's reached the point of diminishing returns at .3uf total.

I then tried doubling C5, which didn't do much besides raise the brightness momentarily while it charged up.

I played with the value of R6, but that didn't seem to do much besides alter the overall brightness.

Also, I just noticed when I turn the set off a spot remains on the screen, which it never did before. But only for maybe 5 seconds, and it's about the size of a quarter, so I don't think it'll hurt anything.

So then I put it back to factory spec, and examined the black levels. Interestingly with the test images I have, they all exhibit perfect black levels until you get to all-black, which is so light gray that it's nearly white. So at least the all-black has some improvement with the new circuit. However when watching actual widescreen video with black bars, it is noticeably worse than it is with the new circuit, that is to say - the changes in black level are more prominent. And also, because of that fade in time with the new circuit, it sort of takes the edge off of rapid light-to-dark and dark-to-light scene changes, by allowing it to slowly fade down or up, so it's not as jarring. So that's good. Which capacitor manages that, though? I changed the values of both of them and it didn't seem to make much of a difference in the fade in time.

Also I measured the crt cathode voltage to ground:
Sam's says: 115
Factory spec: 150
Current circuit: 145
idk, make of that what you will. However I do not have a VTVM, I'm just using a cheap digital multimeter.

Below is attached a schematic of how I have it currently. I understand that it'll never be perfect, but I feel like it could still be a bit better. If you have any more suggestions, I'm listening. And thanks again for all the help!

Oh also, if I should hook up a scope, would I connect to the cathode? And what would I be looking for?

After reading the Rider's TV Manufacturers' cure for retrace suppression, I was kind of disappointed because the resistor numbers do not match the numbers on the Sams schematic. Frustrated, I had put the issue aside. Recently I decided to give it a go again, and through very careful reading and educated guesses, figured out where the connection points were.
(From Rider's TV Manufacturers' Trouble Cures - thanks to bandersen for the link (https://www.earlytelevision.org/rider_cures.html)!)
For 20X1, 20Y1, and 20Z1 chassis:
1. Insert a 270,000-ohm, 1/2-watt resistor in series with the wire connection from pin 2 (grid) of the picture tube to the junction of R317B and C320.
2. Replace R447 (3,900 ohms) with an 8,200-ohm, 1/2-watt resistor and readjust the height and vertical-linearity controls.
3. Connect a .05-uf capacitor from pin 2 (grid) of the picture tube to the junction of C408 and R447.
For the 1st, the resistor and capacitor numbers didn't even matter, as pin 2 of the crt only goes to one junction, so that was it. For the 2nd, the major giveaway was the 3.9k ohm resistor. There are only two in the entire set, and one is like in the tuner or somewhere completely unrelated. For the 3rd, it calls for the junction of C408 and the already-identified R447 and it's a resistor to ground, so it could only be the opposite side.

I'm pleased to say this retrace cure works like a charm. It's perfect, there are NO retrace lines, period. Whereas before it was installed, glaringly obvious retrace lines were onscreen about 90% of the time. I used a .047uf capacitor. I had a .056 ready to try, and even if I put them both in parallel it made no difference. So it's not very picky about that capacitance. Also the old 3.9k resistor tested at 4.5k... makes me wonder how many other resistors have drifted. >_>

I then finalized the DC restoration. I made a tidy little prototyping pcb. Sacrilege, I know. I think it's a much neater solution than perhaps sticking a lug strip somewhere. Plus the fact that it's obviously modern will be less likely to confuse anyone servicing this unit in the future. The schematic posted in the previous post is the current iteration - big thanks to Dobulee for that!

As stated before, it's not perfect dc restoration, but it is an improvement. And it does this thing where a dark scene will start dark and fade to brighter (in about 1 sec). But at least that takes the shock away from the transition. Besides, even without that, it does actually make an improvement in keeping dark levels. However slight an improvement, it was pretty bad without it, so I'll take it.

Next step is putting the chassis back in the case. I've already fixed a couple broken bosses in the case - for the screws that hold the back cover on. And retapped the screw holes on the chassis.

Oh yeah, how would I direct inject video into this? I tried putting raw video right into test point B (I think) which is right before the video amp. It came through but was very faded and gray. Maybe it needs a transistor to amplify the signal? The test point being right before the video amp makes me think that's what it's for.

After reading the Rider's TV Manufacturers' cure for retrace suppression, I was kind of disappointed because the resistor numbers do not match the numbers on the Sams schematic. Frustrated, I had put the issue aside. Recently I decided to give it a go again, and through very careful reading and educated guesses, figured out where the connection points were.

For the 1st, the resistor and capacitor numbers didn't even matter, as pin 2 of the crt only goes to one junction, so that was it. For the 2nd, the major giveaway was the 3.9k ohm resistor. There are only two in the entire set, and one is like in the tuner or somewhere completely unrelated. For the 3rd, it calls for the junction of C408 and the already-identified R447 and it's a resistor to ground, so it could only be the opposite side.

I'm pleased to say this retrace cure works like a charm. It's perfect, there are NO retrace lines, period. Whereas before it was installed, glaringly obvious retrace lines were onscreen about 90% of the time. I used a .047uf capacitor. I had a .056 ready to try, and even if I put them both in parallel it made no difference. So it's not very picky about that capacitance. Also the old 3.9k resistor tested at 4.5k... makes me wonder how many other resistors have drifted. >_>

I then finalized the DC restoration. I made a tidy little prototyping pcb. Sacrilege, I know. I think it's a much neater solution than perhaps sticking a lug strip somewhere. Plus the fact that it's obviously modern will be less likely to confuse anyone servicing this unit in the future. The schematic posted in the previous post is the current iteration - big thanks to Dobulee for that!

As stated before, it's not perfect dc restoration, but it is an improvement. And it does this thing where a dark scene will start dark and fade to brighter (in about 1 sec). But at least that takes the shock away from the transition. Besides, even without that, it does actually make an improvement in keeping dark levels. However slight an improvement, it was pretty bad without it, so I'll take it.

Next step is putting the chassis back in the case. I've already fixed a couple broken bosses in the case - for the screws that hold the back cover on. And retapped the screw holes on the chassis.

Oh yeah, how would I direct inject video into this? I tried putting raw video right into test point B (I think) which is right before the video amp. It came through but was very faded and gray. Maybe it needs a transistor to amplify the signal? The test point being right before the video amp makes me think that's what it's for.

Test points were usually more for measurement than injection back then and even most service/ manufacturing test injection points were not designed with monitor use in mind (composite video as a standard only existed in broadcast studios which didn't buy consumer model monitors)...You want to inject as close to the video detector output as you can while still getting the correct video polarity.

I had this set out on Christmas day running a fireplace and playing xmas music. It performed well, only had to adjust it once a couple hours in, but I was running the contrast right near the point where it's about to make the image unstable, anyhow. I think it's just fine. And the sound is really crisp and clear, even with a couple of weak tubes in the audio section. Something I noticed though, is that it no longer has a spot when you turn it off - the screen just goes black instantly. Which is what it does from the factory, but after adding Doublee's DC restoration mod, it would leave a spot the size of a quarter when turned off, for about a minute.

It just now dawned on me that the retrace suppression circuit was the only change made between then and now. So I guess it kills the spot too. Just thought I'd throw that out there.