Time for a pop quiz! What model of television followed me home today?

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

http://antiqueradio.org/art/temp/Mystery1.jpg

http://antiqueradio.org/art/temp/Mystery2.jpg

I don't know, but I know I will enjoy the restoration article immensely!

CTC-4?

jr

Wow.. Twin speakers..

RCA model 21CT662 director, CTC-4 chassis.
It could be a different model console cabinet or a CTC-4 re-brand, but I'm certain that it is a CTC-4 chassis from owning a 4 myself.

Nice Score.
What did ya pay for it, is the 21AXP22 there working and not gassy, and when do ya plan on restoring it?

Why, of course!! It's "The Director", otherwise known as a CTC-4. Great find. Was watching mine yesterday, live sports. Hope your CRT is as new!
Kevin :D

Nice find - and please, I hope you didn't drink all the Two-Buck Chuck on the way home......:)

Cheers,

Pretty easy quiz, I guess!

A local pet shelter ran a rummage sale to raise funds and this TV (a donation to their sale) was crammed amongst loads of rubbish. After I tried testing the CRT on my Sencore CR70 with no visible signs of life, I offered $60, which they accepted. After thinking it over, I gave them an extra $20.

It's a one-owner local set. All the parts & pieces seem to be there. The cabinet looks better in dim light than daylight, but the decals are unworn and I think the various boo-boos will be easy to touch up. It has the inevitable ding on the brass bezel surround, but I can try the trick (Nick's?) of pushing out the ding as best I can and then putting that brass piece on top where the ding's less noticeable. The grille cloth isn't perfect, but that style should not be impossible to find. The Deluxe logo is all in one piece.

Chassis looks pretty clean after a light dust and wipe. Nothing frightening underneath. I haven't peeked at the flyback yet. The 21AXP22 CRT shows no emission whatsoever on the R and G guns, which I only tested briefly. The filament does have continuity. Tomorrow there will be time for a closer look.

I need more projects like a hole in the head, but this sale was so poorly advertised & attended that I felt like I was rescuing this set from a cruel fate (Goodwill or the dump). I spent about two hours at the sale, between testing things, gabbing with the sales person, and disassembling the set for transport. During that time there was only one other shopper . . . who bought nothing.

Phil Nelson

P.S. The cardboard box in the car held tools for testing & disassembling, not refreshments :)

http://antiqueradio.org/art/temp/Mystery4.jpg

http://antiqueradio.org/art/temp/Mystery5.jpg

http://antiqueradio.org/art/temp/Mystery6.jpg

http://antiqueradio.org/art/temp/Mystery3.jpg

80$ DANG, you STOLE that! I paid 400$ for my barberized Seville....If you ever want to trade for a table model I think we could make a deal.

I would have happily paid them more if I'd had any hint that the CRT is good. I have never seen anything look so dead on this tester. Maybe tomorrow will tell a different story.

Phil Nelson

Nice looking tv, good luck with it !

So, just for the heck of it.... Exactly why do you take the chassis out...? Not much of a weight savings moving the cabinet.... If all the bolts are there it ain't gunna move... They were surely shipped in one piece from the factory.... When I was a kid I moved floor model sets on a lawn mower bottom with the tv up side down for miles, and never lost anything..... And when I got my zenith roundie it only had one nut in the chassis, I made reasonable sure it wasn't gunna hit the tube, and off I went... So I really don't get all the work takin out the chassis....?

I don't think I would have stood around testing the tube either.... Just load it up and get outa-there before someone else showed up who might have wanted to start a bidding war on it cause he thought he could resell it on ebay for more....

Its very clean inside...... really nice..... Christmas came early fer you....

Did ya get up and pinch yerself today yet....?

I guess its good to have a minivan in the stables..... I got my 9t240 in my '86 prelude, almost didn't fit in the front seat.....

Phil, send me the serial number for our database. Nice find.

Wow, nice find! It's must have been stored in good conditions; even the yoke cover is in fine shape. I sure hope the CRT comes back to life!

It is very clean. I was told it never left the owner's living room since new. It has some replaced capacitors underneath and I found a couple of little solder splashes on the floor of the cabinet. I suspect that whatever service it got was given right there in the lady's house.

Exactly why do you take the chassis out...?It's too tall to stand up in my SUV. I know because I transported my (much shorter) CTC-7 upright in that vehicle and it barely cleared the ceiling. There was nobody to load it but skinny old me and the lady running the sale. (She was also baby-sitting a toddler and two dogs, but they were more trouble than help.) I didn't want to chance dropping it or gouging up the front while grunting it face-down into the back.

Steve, the serial number is B8085878.

Phil Nelson

http://antiqueradio.org/art/RCACTC-4SerialNumber.jpg

Great find Phil. Look forward to reading your comments as you restore the set. Hope you can wake up that CRT.:boring:

-Steve D.

Testing the CRT with my Sencore CR-70 doesn't have me dancing, so far. I measure .7 ohms between pins 1 and 14, so the heaters are not completely open.

Before connecting the universal adapter to the CRT, I set the heater voltage to 6.3. When I connect the UA clips to the pins and turn on the tester, the voltage drops to around 3 volts and the CR-70 makes a high whining noise. If I disconnect a heater pin, the noise goes away and the voltage goes back to normal.

The CRT passes the H-K shorts and G1 shorts test, but the needle doesn't move at all for cutoff test or emission test. This is the same for all three guns.

Suspecting operator error, I double-checked the manual and looked at an old photo of my tester connected to the 21CYP22 in my CTC-7. With exactly the same settings, the tester worked normally and checked the emission, etc., for each gun in that tube. I even hauled the tester out to check a B/W tube, and the tester works normally.

Not sure what is going on here. For an old B/W tube, I'd just let it sit on the tester for a while, to see if it wakes up under normal or slightly elevated filament voltage. I don't see any glowing inside the base, but the base is getting warm.

Phil Nelson

http://antiqueradio.org/art/RCACTC-4CRTNumber.jpg

http://antiqueradio.org/art/RCACTC-4CRTCheck.jpg

Can you actually see the heaters lit inside the neck?

Unfortunately, continuity but drawing excessive heater current and not lighting up sounds an awful lot like the tube has gone to air. Can you pull some of the neck components loose to get a look at the getter flash?

Sounds like air. The getter is under the yoke somewhere, a slotted area around the neck provides a window to view it.

Selenium rectifiers AND a power transformer? Usually Selenium rectifiers are used in hot chassis sets, and transformer sets have tubes like 5U4 for the power supply B+ production. Or are these seleniums used for another function?
http://antiqueradio.org/art/temp/Mystery2.jpg

Hopefully the CRT's vacuum hasn't leaked out.

The base getting warm that quickly certainly points to air.

:tears:

Area inside these slots looks milky :(

Phil Nelson

http://antiqueradio.org/art/RCACTC-4CRTGetter.jpg

http://antiqueradio.org/art/RCACTC-4CRTGetter1.jpg

Selenium rectifiers AND a power transformer?Yes, similar to the CT-100.

Phil Nelson

Seems like an air dud. Sorry it's gone to air. :tears:
Anyone ever install a 21CY in a CTC-4 without modifying the mask area, or other mounting hardware? I know about cutting the yoke flange when using an FB.
Kevin

Seems like an air dud. Sorry it's gone to air. :tears:
Anyone ever install a 21CY in a CTC-4 without modifying the mask area, or other mounting hardware? I know about cutting the yoke flange when using an FB.
Kevin

Cutting the yoke flange for a 21FBP22?! I still entertain hope of getting a good AXP for mine so I just used a modern cup HV connector and stuck several layers of a THICK plastic bag between the yoke and HV connector area to prevent arcing/corona...It works fine, and I did not hack up any OEM parts.

Too bad, the 21AXP22 went to air. You paid less than I did for my Director, I think it was $125 and I had to drive to Indy to get it. Great scroe!

So, I guess the CRT replacement options are pretty limited . . . .

Phil Nelson

Phil,

We have the technology to locate the leak with the Helium leak detector. The leak will be located somewhere on the weld where the front and rear sections of the tube are welded together.

I believe Nick did some welding recently on some part of a 21axp22 that he is playing around with and commented that the material welded suprisingly easy.

So if we are able to locate the leak (which is easy) and Nick can re-weld the area where the leak is located, then it should be an easy task to re-gun the tube some day at ETF. I know somebody who has a stash of delta guns in the event we are able to get a rebuilding plant up and running at ETF some day.

Moral of the story is SAVE YOUR LEAKING 21AXP22 crt's. We might be able to fix them some day.

BTW: there is so much air in that tube that I can see corrosion on some of the gun elements.

The AXP in my CTC-4 is gassy so I used a 21FBP22 as a substitute, and I can tell you it does work.
Any 21" good roundy color jug will work. With the glass jugs you need to remove the plastic CRT cover, make a new HV lead/plug, unscrew all the screen purity magnets so they are as far from the screen as they go, and ground the CRT's dag. On the non-21CYP22 tubes(I can't speak for the 21CPYP as I've never owned one) you will need to put some thick plastic between the metal yoke shell and HV connection on the side of the CRT to prevent arcing(because the grounded yoke will practically overlap the HV connector) According to a previous post I guess that some collectors prefer to cut a notch out of the yoke shell instead of using insulation to prevent arcing.

I'm not going to try to find my thread now, but to give you an idea of how good a deal you got...I shelled out over 400 clams for my CTC-4 pictured here http://s1095.photobucket.com/user/ElectronicMemory/library/RCA%20CTC4%20Seville%20%20blond%20finish?sort=3&page=1 , and I have seen nice 4's on the bay go for north of a grand.
My restoration is on hold now as I moved and since then I have not been able to clear enough bench space to work on it....That and it has IF/AGC intermittents and alignment problems that I don't have the experience or equipment to properly address at present.

There was something else I was going to say, but I'm so groggy right now that I for got it as I was typing the last sentence...

EDIT: Bob's post jogged my memory. I was going to say the 21AXP22 CRT's are about as bad about going to air as the 15GP22....Only there is not as much of if any effort to create a successful rebuilding process.

PS: I'm saving my AXP and it's plastic insulator for the day when they can once more be rebuilt.

Thanks, that sounds more encouraging. This set has a lot of potential. I really want to restore it to operating condition, not just keep it around as a doorstop.

Phil Nelson

Thanks for the SN, Phil. Your set is now in the database.

The CTC4 was a good performer, much more robust than the CTC5s.

Too bad about the crt. Electronic M has a good point, put the tube in plastic, better yet, do what you can to bring it down to a vacuum and then seal it. Even if all you can do is HVAC level vacuum, heat it too and boil out as much water as you can..... Then seal it.

Too bad about the crt. Electronic M has a good point, put the tube in plastic, better yet, do what you can to bring it down to a vacuum and then seal it. Even if all you can do is HVAC level vacuum, heat it too and boil out as much water as you can..... Then seal it.

I did not seal mine in plastic. There is a plastic CRT insulator to keep prying fingers from touching the metal bell. That insulator is unnecessary with a glass CRT so I have it stored on my removed, dead AXP. Mine still holds some vacuum so I plan to leave it be.

If I was in Phill's position (with a tube that is completely down to air) I'd remove the base and the pinch-off stem and try to fill the tube with a noble gas that is heavier than air. Noble gas is non-reactive(unlike air) so it would be chemically about the same as having the tube under vacuum and, as long as it does not leak out, would preserve the phosphor and metals inside the CRT preventing further corrosion. After filling it through the pinch-off I'd store it face down and seal the pinch-off with caulk or some such.

Sorry, I misunderstood you.

As to Phil's tube, Any chemical is likely to out-gas something that can react with the phosphorous so I would not seal it with anything but hot wax. I did see in his photos, that he is correct, it does look like some of the elements are corroding.... Since its corroding in the gun area, I wonder if the leak is down there as well... Like at the metal pinch off...?

Anyway, my original thought still is what I would do, Put it in a box, metal, glass, plastic, heat it to 90 degrees, pull a vacuum for a few days, then seal it. If you find the leak, and its down at the gun, then even better, seal it there after trying to get the moisture out.

Unfortunately, if the tube has been down to air long enough for the gun to start rusting, it may already be a goner. Back when CRT rebuilding was a viable option, rebuilders would generally not accept duds that had lost vacuum, as they weren't considered rebuildable.

The aluminum coating over the phosphors is likely corroded as well as the shadow mask.

As soon as the air came in, the oxide cathode coatings started absorbing CO2 from the air to form inactive carbonates.

At the very least, the gun will need to be replaced. But if the mask or screen is damaged, the tube is worthless.

Well why don't you just poop on our parade..... : )

Still have to wonder how long it took to form rust on the gun....?

I would still vacuum it and seal it... Even as a test, you gotta give it every chance as the number of usable duds still needs to be protected....

Well, when the ETF rebuilding project gets off the ground, maybe I can donate this 21AXP22 as a test subject.

Meanwhile, I guess I'm in the market for a 21" color tube that can be adapted to work in this TV. Anybody got a spare?

Phil Nelson

While all of the above seems logical in regards to elements being damaged by exposure to air, keep in mind that RACS in France when they were still in business a couple years ago successfully rebuilt a necked 15gp22 that was exposed to air for many years. The screenshot after rebuilding seems to indicate that air did not cause any damage to the mask or phosphors.

While all of the above seems logical in regards to elements being damaged by exposure to air, keep in mind that RACS in France when they were still in business a couple years ago successfully rebuilt a necked 15gp22 that was exposed to air for many years. The screenshot after rebuilding seems to indicate that air did not cause any damage to the mask or phosphors.

Well there ya go-

Better take steps to protect this dud from further oxidation....

IIRC there were some poor condition phosphor patches (could have been caused by water dripping in) on the necked RACS tube...It was not ruined but it was not perfect either.

I still think a noble gas is better than a vacuum. You can probably get something heavier than helium for about the same price(making it cheaper than sourcing any usable vacuum pump and suitable accessories). Also consider that if you have a poor vacuum (not as good as factory) there WILL still be many corrosive air molecules inside...Make that trapped inside where they will continue to corrode the tube. Noble gas does not react with anything (anything includes metal, glass, cathode surface, and phosphor), and thus will not cause corrosion or degradation to the CRT. If the tube is stored face down, the gas is poured in through the neck, and the gas is heavier than the main constituent gasses in our atmosphere then the noble gas will sink to the bottom of the tube and slowly displace the air upwards and out through the neck. Think of this filling process like like filling the tube with water(don't fill your tube with water), the noble gas has a similar comparative density to air as does water so as you introduce noble gas gravity and negative buoyancy (relative to air) forces it to the bottom and it fills up the tube from the bottom as if you were pouring water in. If the leak is in the face the noble gas may slowly leak out (if the leak is only big enough for air molecules to pass through then heavier and thus larger noble gas molecules won't get through), but if the tube is face down a lot of gas would have to leak out before air could again reach the shadow mask and phosphors. The shadow mask and phosphors are the most critical part to preserve as they are the least replaceable, and permanent damage to them will affect the picture quality of a rebuild more than any other part that can be damaged by air.

For the noble gas idea to work, you have to know what the oxides will do with those gases present, and know for sure nothing bad can result as the moisture will remain because you have done nothing to deal with it. Bringing a HVAC vacuum and 90 degrees heat will cause the moisture to boil off as its boiling point is greatly reduced. Then if nothing more, you put the tube in a very thick heat sealed bag with a desiccant inside the bag of sufficient size to do some good, and then keep an eye on it as they change color with moisture (as they absorb it). How will you know if the noble gas leaks out ??

There is no reason why people here can't build a drying for storage box where you mail it to whomever needs it, and heat and vacuum the tube for storage, then bag seal it with desiccant for long term storage. You could get a local HVAC guy to run a vacuum on it.

Nice score.

Vans are nice. I couldn't even fit a 20" Zenith in the trunk of my '11 Impala today.

I have a line on a good 21FBP22, thanks to a helpful VK member.

I'm open to ideas about how to preserve this 21AXP22 in the meantime, although building vacuum chambers or bake boxes doesn't seem likely. My workshop is in an uproar during some remodeling and half its contents have already been evacuated into other parts of the house.

Phil Nelson

I don't think the phosphors are in any danger, as long as no liquid water got in there. That 15G RACS rebuild was a wreck and a half sitting around with no gun in it at all, and it's still working just fine to this day. If you wanted to be sure though you could cleave the gun out, then purge it with a slow flow of nitrogen over a few days to displace the air.

I have a line on a good 21FBP22, thanks to a helpful VK member.

I'm open to ideas about how to preserve this 21AXP22 in the meantime, although building vacuum chambers or bake boxes doesn't seem likely. My workshop is in an uproar during some remodeling and half its contents have already been evacuated into other parts of the house.

Phil Nelson

Hi Phil ,

In reading your post about not being able to easily build a vacuum chamber or bake box I got to wondering about the tube's physical position during storage . Specifically , would it make sense to store it in a position of having the screen up and the gun down , opposite of the normal way they come when new in their boxes ? (any new CRT I've ever unpacked was always "face down" in the carton)

I ask this with the idea that if there is enough moisture to rust the gun , and folks have mentioned possible phosphor damage , maybe with it stored screen facing up no moisture will be able to drip off of the gun and damage the phosphors ...

I'm not a good enough scientist to guess whether dripping is a possibility, or whether the rusting resulted from moisture in the ambient atmosphere. I could probably build a box with sturdy supports to hold it face up, if that seems important.

Whatever I do will need to be fairly low-tech. For instance, I could store it in a sealed plastic bag with some dessicant gel.

Phil Nelson

The gun isn't the problem, it's the shadow mask. If that has rusted or deformed, the tube's junk no matter how many guns you put in it. Getting the old gun out would confirm the extent of the damage, as you'll be able to see down the neck and have a look at the condition of the mask.

And yes, I can weld these tubes successfully. If there's a leak, it would be a lot easier to fix than on a 15G. With the 15G you'd have to frit treat the glass/metal joints first, then weld the metal seam of any pinholes.

Phill,

Leave it alone. Don't mess with it. Just put it in storage in your climate controlled home until such time as it may be a candidate for restoration. It is still sealed good enough that it is better than anything that you could possibly do to improve the situation.

Moisture is likely not the issue. The tube has O2 inside, and when the gun was heated via the filiment, the metal on the gun reacted with the O2 and caused oxidation of the metal in the guns elements. If the filiments had not been heated in the presence of the O2 in the tube, then it is very likely that the gun elements would not have oxidized.

Anyhow, no harm done. The gun is toast in any event and would need to be repaced or rebuilt if the tube is ever to be rebuilt after fixing the leak.

Best way to get a usable 21AXP22 is to wait for a clunker CTC5 to surface to steal the crt out of. The 5's still surface once in a while and I would personally rather have an opperational 4 than a clunker 5. The 4's have a better picture quality.. I have actually trashed a crappy 5 and made a 21AXP22 test jig from the crt, and associated cabinet components. Some day I will likely use the crt from the test jig to restore a worthy set needing a 21AXP22.

Be patient and sooner or later you will come by a decent usable 21AX for your director. I would presonally NOT do a retrofit with a glass tube. But that's JMHO, and my way of doing things. I would rather have a correct bad tube in a display set than an incorrect tube in a functioning set.

Thanks for the advice. If I can fit a glass tube non-destructively and watch the TV while I'm waiting to find the right tube, that would make me happy.

Does anyone happen to have the RCA factory manual? I have the RCA field service manual and an RCA service data supplement, but not the manual itself (Service Data 1955 no. T5). These docs (plus Sams) give me enough info to restore the set, but you never know what handy little tidbit another manual might include. I'd be happy to pay postage & a reasonable fee to borrow one for scanning.

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

After replacing the electrolytic & paper capacitors, plus assorted resistors, the chassis passed the smoke test and has reasonable B+ and filament voltages. After I lay my hands on a couple of new tubes and oddball caps, I'll be ready to try more interesting experiments.

Looking ahead to when/if I get a usable 21FBP22, I gather that I'll need to fabricate a new HV lead for the CRT 2nd anode and make some provision to prevent arcing from the anode button area to nearby hardware. I'm hoping to use the same yoke and other neck whatnots, since nothing else is available. If that's a false hope, someone tell me now!

Phil Nelson

Last year there were at least two 21FBP CRTs for sale at the ETF so chances of finding one are good. Nick (AKA miniman) told me when I bought my set from him that on another CTC-4 he has for a time he had a glass tube in it and there was a scope HV lead that either worked straight up or at least had the correct plug to plug into the HV cage. I took the lazy path and used a salvaged BPC TV HV wire and carefully stripped a long section on the end of the wire, folded and soldered it until it would mesh with the female HV connector on the HV cage. and I sandwiched some thick plastic bags between the yoke and the HV connection on the CRT and the yoke.
It ain't the prettiest metal to glass CRT conversion, but it DOES work just fine.

You can do the metal to glass CRT conversion. Others have made it work in the past so there is no reason that you can't.

Tektronix scopes have the tower connection you need, but the glass tube anode does foul the yoke support causing arcing. You can try to insulate it somehow, cut the support to gain some clearance, or rig up your own crt mounting system.

Speaking of arcing, in the HV cage the 22-ohm resistor was burned and broken and the hood for the 6BK4A regulator tube was nibbled away, with evidence there had been arcing through the hood to the inside of the cage. I scrubbed the hood inside and out when I replaced the resistor and the electrolytics. Let's hope that puts an end to the fireworks.

Phil Nelson

http://antiqueradio.org/art/RCACTC-4HVCageUnrestored.jpg

With a couple of new tubes, now I have great audio and decent sweep waveforms, plus a reasonable stair-step waveform at the video amp when I supply a color bar signal. Here's one of the horizontal waveforms:

http://antiqueradio.org/art/RCACTC-4FirstPower.jpg

Too bad my CRT is a dud!

Phil Nelson

Signs of life...I bet it makes high voltage, try it out.

Yah, it makes HV. This looks like about 19.5 KV. At the moment I'm running it from an Isotap at 110 VAC line voltage.

http://antiqueradio.org/art/RCACTC-4FirstHighVoltage.jpg

Had to scrounge for something to defeat the HV interlock. This cap from an old Disneyland pen did the trick!

http://antiqueradio.org/art/RCACTC-4HVInterlockDefeat.jpg

This chassis seems very stable. I feel like I could be watching a movie tonight if I had a usable CRT. There are other things I can do in the meantime, but none of them half as fun as seeing that first image on the screen.

Phil Nelson

It really needs to be run at 117 VAC, that will stiffen it up quite a bit. Mine had the seleniums replaced with silicon diodes and a dropping resistor, so it's probably a little stronger than yours in HV production. I have mine set to around 24kv on the anode, but it will go much higher if you let it. Have you gone through the horizontal circuit setup procedure yet?

I haven't done anything besides power it up at reduced voltage and take a few readings while watching out for smoke. After the holiday, I should have time to replace the seleniums and start on all that other good stuff.

Phil Nelson

Thanks to the generosity of another VK member, I have a 21FJP22A with good emission. It arrived yesterday, in my homebrew CRT box that I shipped to him empty. He popped in the CRT and sent it back, and it arrived here in fine shape.

http://antiqueradio.org/art/RCACTC-4CRTBoxArrived.jpg

I haven't tried anything on for size yet, since the cabinet is completely disassembled, but I guess some people would cut a notch out of this retaining ring to avoid fouling the 2nd anode lead on the new CRT.

http://antiqueradio.org/art/RCACTC-4CRTRetainingRing.jpg

It may be a while before I get to try out this CRT with the chassis. During our remodel, my workshop is packed into 100 boxes and temporarily piled in our new garage, which doesn't have power yet. Our living quarters are so crammed with overflow that I had to unpack the CRT in our front entry -- and then clear away all the mess before dinner guests arrived.

Phil Nelson

I previously posted this RCA production line photo to ETF. For those that have not seen them I'm posting them here as well. Phil, perhaps one of these is your CTC-4 "Director".

-Steve D.

Wouldn't it be cool if mine was one of those? Wonder what "adjustments" those experts are doing in the publicity photo? Checking to see if the top covers fit?

Phil Nelson

Wouldn't it be cool if mine was one of those? Wonder what "adjustments" those experts are doing in the publicity photo? Checking to see if the top covers fit?

Phil Nelson

Good one Phil. The photog probably told them to look busy. Here's another photo of the CTC-4 production line I originally submitted to the ETF site.

-Steve D.

How much was the cost to ship the empty box?

Always wondered.....

SR

I cost just under $180 to FedEx the empty box coast-to-coast. It's the size that made it expensive; the shipper told me it could have weighed up to 200 pounds without increasing that charge. (UPS would have cost even more, if you're wondering). My box was about 2-3 inches taller than it really needed to be. I don't know if making it shorter would have gotten it under some size limit.

I couldn't resist setting the new tube into the cabinet and trying on the retainer ring.

http://antiqueradio.org/art/RCACTC-4NewCRTWithRetainingRing.jpg

That anode connection is awfully close to the ring. Seems like you're asking for trouble (arcing) if you don't cut away some of the ring.

Looking ahead to when I really install it, the tube has an aquadag coating, so I guess that means fashioning a ground connection.

I don't have any use for the old insulating skirt. I wonder if it would be useful to cut away the bottom of the skirt and retain the rest (the waist, if you will) to go between this ring and the tube's neck and bell? I could even pigtail onto the old ultor connection -- which is built into the skirt -- to make the new aquadag connection. (I already cut off most of the old ultor lead to make my new anode lead.) That would mean cutting a hole in the skirt for the anode lead, of course.

On the other hand, if I butcher the skirt, I couldn't reuse it in the remote event that I run across a good 21AXP22 or have mine rebuilt . . . .

Phil Nelson

Interesting stuff.
For a dag connection use flat braided wire with a spring to pull things tight.
Anode is too close, cut out a large half moon. Insulate with a
piece of plastic with a channel, get from a 70's era Zenith. Others
may have used them, dont remember. They went on the DGS shield.

Use the large brown single wire anode connector from a Zenith tripler
like a 221-141-**. Very common & the heaviest anode I remember.
We used them for all replacements. PN's are 15-276 & 15-276-01
one has 2 holes for HV & focus divider & the other just one hole.
Most had a screw to put them on.

73 Zeno:smoke:

I cost just under $180 to FedEx the empty box coast-to-coast. It's the size that made it expensive; the shipper told me it could have weighed up to 200 pounds without increasing that charge. (UPS would have cost even more, if you're wondering). My box was about 2-3 inches taller than it really needed to be. I don't know if making it shorter would have gotten it under some size limit.

I couldn't resist setting the new tube into the cabinet and trying on the retainer ring.

http://antiqueradio.org/art/RCACTC-4NewCRTWithRetainingRing.jpg

That anode connection is awfully close to the ring. Seems like you're asking for trouble (arcing) if you don't cut away some of the ring.

Looking ahead to when I really install it, the tube has an aquadag coating, so I guess that means fashioning a ground connection.

I don't have any use for the old insulating skirt. I wonder if it would be useful to cut away the bottom of the skirt and retain the rest (the waist, if you will) to go between this ring and the tube's neck and bell? I could even pigtail onto the old ultor connection -- which is built into the skirt -- to make the new aquadag connection. (I already cut off most of the old ultor lead to make my new anode lead.) That would mean cutting a hole in the skirt for the anode lead, of course.

On the other hand, if I butcher the skirt, I couldn't reuse it in the remote event that I run across a good 21AXP22 or have mine rebuilt . . . .

Phil Nelson
Sylvania published a brochure back in the late 60s about installing rare earth tubes in older receivers titled "Color Fidelity for Older Receivers". The part on CTC-4 showed a small portion of the skirt cut away from the anode area of a 21FB to allow for the connection of a compatible lead and boot. I scanned it, and have it somewhere, but not on this machine. I'll look for it tomorrow and if I find it I'll post it here. Should be an easy job to do, and will prevent arcing. I'm considering putting a 21CY in my CTC-4 but haven't yet made up my mind about that. :scratch2:
Good luck Phil!
Kevin

Phil,

When I purchased my CTC-5 Wingate, many years ago, the previous owner had already had the 21AXP22A tube replaced w/a 21FB22. RCA provided a conversion kit that allowed for the installation with a retaining ring that attached directly to the rear of the mask. No struts required and plenty of clearance room for the anode lead. I don't recall ever seeing another kit like this in other sets.

-Steve D.

Thanks, that is excellent information. I wish I could install the CRT and try to fire it up tomorrow, but with so many things packed up and no suitable place to work, that ain't gonna happen. At least I can try to collect the right materials in the meantime.

Phil Nelson

Phil,
I couldn't find the original brochure, but I did find a scanned copy in my CTC-4 binder. The scans aren't too good, but can be read. At least the recommended dimensions are given for notching the flange, along with advise about supporting the bottom of the mask assembly, as the glass tube is much more heavy than the 21AX.
Kevin

On my CTC-4 I was able to get away with not cutting the skirt and instead use a modern anode lead salvaged from a 90's BPC set and a few layers of thick plastic ziplock bag type material stuffed between the skirt and the HV suction cup. Back when I was active with that project it did not seem to allow any arcing or corona.

I feel it is best not to cut or modify any of the original mounting hardware as you never know when a good 21AXP might surface. Going with that thinking I saved the unmolested bell insulator as is from my set and refrained from cutting the HV lead to have the plug. I was able to make a decent HV plug by striping a good length of spare HV cable folding the wire neatly and tinning the strands together with solder....There are better solutions to the plug then I implemented, but my way does work.

With how perfect your set is I strongly encourage you to not do any thing permanent to mount a different type of CRT which may end up only being a temporary substitute.

Yes, I'm always in favor of the least-destructive solution. Today I laid my hands on a modern anode lead. Perhaps I will try that with some insulating layers between the anode cup and the metal ring (and one hand hovering over the power plug).

Phil Nelson

Good suggestion, Tom. I also would like to keep my 4 as original as possible. I installed a 21FB in a CTC-7 once, and used a Cool Whip top cut in half with GC high voltage putty between the halves. I wedged it between the ring and the CRT with great results, no arcing. I know Cool Whip is still available, but I don't know about the putty. I'm pretty sure a sub could be found to work. :yes:
Kevin

I tried using just a modern anode cap all by itself on my set before I had a good 21AXP22, but it would create random loud telltale 'snaps' as it would arc right through the silicone. 25kv ain't nothin to fool with, I would either cut the support you have or find a very slim anode cap and add additional insulation.

Phil,
I couldn't find the original brochure, but I did find a scanned copy in my CTC-4 binder. The scans aren't too good, but can be read. At least the recommended dimensions are given for notching the flange, along with advise about supporting the bottom of the mask assembly, as the glass tube is much more heavy than the 21AX.Yes, I had never lifted a metal tube before and I was startled at how much lighter it is than the glass counterpart.

I might be able to get that article through an inter-library loan (to make a better scan) if I can tell them the desired issue. As I read the first page, it is Sylvania News Technical Section, Summer-Fall 1965, volume 12, no. 2.

Phil Nelson

I think you can still buy Cambric insulating cloth from Antique Radio Supply. This stuff is great for HV insulation. I would put several layers of it under the bell and over the anode connection. This way you don't destroy anything original.

Any chance you could find a spare skirt ring from someone else's junker set to hack up and preserve your original?

Sure, if someone has a spare metal retaining ring, I'd be delighted to use that in place of mine. On the other hand, this was a "factory approved" sort of modification, which seems less objectionable than hot-rodding an old TV. If I just cut an arc out of the ring, it should still work to support a much lighter 21AXP22.

That cambric insulating cloth sounds interesting, but I'm not finding it on the AES website. 3M makes a varnished cambric insulating tape that's rated for 69KV but quite expensive. This 3M splicing tape is also good for 69KV and cheaper:

http://www.grainger.com/product/3M-Splicing-Tape-4YT49?searchQuery=4YT49&fromCatalog=true

If you don't remove a piece from the retaining ring, I guess the idea would be to get as much insulation as possible in the small space between the anode button and the metal ring.

You could also put insulation under the retaining ring to isolate it from the bell of the CRT. As I understand the original setup, the big ring with the convergence magnets connects to ground, but the retaining ring and yoke support are left to "float" electrically. They are insulated from the CRT by the big plastic skirt, and the long retaining stays connect to the wooden cabinet with staples anchored in thick ceramic (or plastic?) washers.

Phil Nelson

P.S. I just remembered that I have a little jug of corona dope somewhere in my boxes of stuff.

It shouldn't take much insulation. Remember that the plastic ring that is around the rim of the metal tube is less than 1/8 inch thick.

I want it! I want it!! Yes, for real, I want it!!!

I couldn't resist messing with the set a little. Steve was right, it didn't take a ton of insulation. I cut a small notch in the retaining ring and covered the edges with a few layers of this tape:

http://antiqueradio.org/art/RCACTC-4VarnishedCambricInsulatingTape.jpg

The 21FJP22A tube survived its cross-country journey and it lights up OK. Strangely, I somehow lost signal since the last time I powered it up on the bench, when I had nice audio and I could see a video signal (with a scope) at the video amp.

http://antiqueradio.org/art/RCACTC-4FirstLight.jpg

No doubt it is something simple, but it's too late to investigate tonight. Anyhow, the CRT conversion was simpler than I expected.

Phil Nelson

P.S. No, I haven't yet played with purity adjustments or any of that other good stuff.

No doubt it is something simpleOr maybe not. The no-signal condition persists, as if there's nothing coming out of the tuner. I found that I can connect everything if I stand the chassis on our trusty old cooler. Not convenient, but I'm lacking a workshop at the moment.

http://antiqueradio.org/art/RCACTC-4LameSetup.jpg

Injecting a video signal at the video amp gives me a faint picture.

http://antiqueradio.org/art/RCACTC-4FirstCrossHatch.jpg

Injecting an IF signal in the IF strip also gives a (fainter) picture.

http://antiqueradio.org/art/RCACTC-4FirstTestPattern.jpg

Subbing the 6X8 and 6BQ7 tubes in the tuner changes nothing. I still get absolutely nothing from the tuner -- no static/scratching when you change channels, nada.

I guess the next step is to pull the tuner and try some cleaning. I'm still at a loss to see why the signal suddenly disappeared. There are no obviously torn-loose wires, etc.

I posted the Sams manual here for anyone who's curious:

http://antiqueradio.org/art/RCA-CTC4-Sams-314-9.pdf

I believe the schematic from my RCA field service manual is more accurate, but I don't have a scan of that.

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

Try wiggling the IF and AGC tubes, and adjusting the AGC control. Part of the reason I shelved mine mid-resto (asside form it needing and alignment that I'm not equipped for or experienced at) was that the IF sockets in mine were intermittent and so was the AGC...I could loose all signal if it was in a bad mood on a given day.

Wiggling every tube in sight got me nowhere, but after cranking up the AGC control I'm getting a healthy scratch (visual & audible) when I change channels. Maybe cleaning the tuner will help. I don't see any easy snap-off panel that can be removed. I guess you need to unsolder the connections and remove the whole tuner assembly.

Phil Nelson

P.S. I did go through my usual routine of cleaning all tube pins & sockets at the start of this project. I suppose it can't hurt to re-clean the sockets in the tuner & IF, etc.

IIRC I was able to clean my tuner without electrically disconnecting it, but it has been about 3 years since I did that....I think a number of screws have to be removed to get the cover off.

Sockets were the culprit in mine as well, so that makes 3. I also had an AGC pot that was smoked, that sure didn't help. I'm still trying to get my audio back, I lost it at some point and it's been on vacation ever since.

To fix the sockets, you can sort of repin them with new contacts from another socket. You have to be careful and do them one at a time in situ, but when you're done the job is worth it not to have bum connections on the PC boards.

I also had an AGC pot that was smoked, that sure didn't help.
To fix the sockets, you can sort of repin them with new contacts from another socket. You have to be careful and do them one at a time in situ, but when you're done the job is worth it not to have bum connections on the PC boards.

What type of sockets did you get the new pins from?

I'll have to test the AGC pot when I get back around to my CTC-4.

Vigorous socket re-cleaning changed nothing. Next stop, Tunerville.

http://antiqueradio.org/art/RCACTC-4TunerCoverRemoved.jpg

Removal meant unsoldering ten connections, but they were all easily accessible. I will carefully clean the contacts with swabs and liquid DeOxit.

Phil Nelson

If the video amp is after the tuner, signal path wise, why would a weak picture(while injecting at the control grid of the video amp) mean that the tuner was bad? Not saying it isn't, I'm just not following the sequence of events I guess. :scratch2:

I was just walking backward, doing a very basic check to see what sections could pass a signal. Seeing a picture when I injected video at the video amp suggested that things downstream from there were working (at least marginally). Seeing a picture when I injected an IF signal at the IF amp suggested that things downstream from there were working. So, the no-signal problem was likely between the antenna terminal and the IF strip.

The solution was simple, after all, and it turned up when I serviced the tuner. The UHF-VHF switch in back of the tuner was funky and it had stuck in the UHF position. Here is the switch working normally:

http://antiqueradio.org/art/RCACTC-4UHFVHFSwitchAnimated.gif

I'm not impressed with that switch, or the quality of the tuner in general, but it's all clean and operational now, and I can get a picture through the antenna input.

http://antiqueradio.org/art/RCACTC-4TunerCleaned.jpg

And now for that Wizard of Oz photo you've been waiting for!

http://antiqueradio.org/art/RCACTC-4FirstWizardofOz.jpg

Yah, we're a long way from a good color picture, but the CRT transplant was successful, knock on wood, and I think there's hope for the old girl, after all. Now to read up on CTC-4 setup procedures . . . .

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

Looks like they could have done a little more work on the design of that switch....
Movement to the right those contacts hardly get anything to stand on....

Anyway, nice job on the animated gif....

Have you not degaussed the tube yet? or not done any purity? <-- Sorry re-read above posts...

Nice bright tube though....

If you come across an original tube, will you put it back in...?

Hi Phil, thanks for your patient reply to my video amp question, and sorry for the "senior moment" on my part.

Ditto on the "nice job with the animation", and with the super job cleaning that UHF switch. Seems really odd that RCA wouldn't have spent just a tad more on it given the expense of a color set in those days.

That wicked witch is looking badder all the time. LOL.

Well, I'm making slow progress. The B/W picture is very watchable -- good contrast, brightness, focus, geometry. I worked through the purity drill and all seemed well. Got nice clean red, blue, and green rasters. Those big magnets in the field neutralizing ring are pretty fun to use and they work well. I made the convergence decent in the central zone. It's not so hot around the edges, but there will be more time to play with all those dynamic convergence controls later.

When I display color bars or play a DVD, there is basically no color, even with the killer threshold turned all the way down and the color control turned all the way up. The AGC control seems to operate as it should. I tried tweaking the oscillator on one channel and convinced myself that fine tuning is not the issue.

Tomorrow is another day. I guess I will start at the color takeoff (chroma bandpass amp) and start working downstream, looking for problems in the color path.

As for using a 21AXP22, you bet I'd use one if I found one. I'd drive a 1955 Corvette if I found one of those, too, but meanwhile, we make do with what's on hand :)

Regards,

Phil Nelson

Since you will be working at this for awhile I decided to send you something to help aid in servicing your chassis
:)

Good luck on the convergence Phil, I got mine watchable and left it.

decided to send you something to help aidA bottle of Valium?

Convergence isn't so much an issue as the absence of color. I could see colored dots on the screen when doing static convergence, and see colored rasters when doing purity, but now it's basically black and white except for color fringing in the edge areas with bad convergence.

I have had to pack the whole thing away for a while. Having this project spread all over the kitchen was [A] not an efficient way to work and [B] giving us both a nervous breakdown.

Phil Nelson

These things can really beat a person up trying to find problems.
I know how that is.
make a short Extension for the Yoke for now, parcel post to Washington is about 4 days.
I remember this chassis from a few years ago when I owned one.
the Kitchen is the best place to work on !

This TV languished for a long time while my shop was torn up for remodeling, but now I'm running out of excuses and should get back to it. Perhaps I'll start with purity and work through the color setup procedures. After I gave it a 21FJP22A transplant, I left the purity magnets cranked all the way out, and the purity is about as bad as it can get.

Which reminds me: I got a copy of the big 91-page CTC-4 RCA service clinic manual from the ETF and scanned it. I figure ETF will put it in their schematic archive, but you can also download it from this URL:

http://antiqueradio.org/art/RCA%20CTC-4%20Television%20Service%20Manual.pdf

The manual has schematics for early & late production, plus lots of other goodies.

Regards,

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

What an awesome document to make available!

Thank you for posting that service manual, Phil. One day I will proceed with my own CTC-4, after the kitchen remodel in progress now.

Back to the TV, I just worked through the preliminary purity & convergence adjustments, and saw plenty of R-G-B in the raster, dot, and crosshatch test patterns. No surprises. Then I switched to a color bar pattern and saw . . . shades of gray.

Same monochrome result if I play a DVD or receive a broadcast on rabbit ears from the in-house modulator. I adjusted obvious things like the color control, color killer & noise inverter, AGC, and so on. I also tested the obvious tubes, which are all fine.

When I use the fine tuner, it's as if the tuner is not centered on the frequency. Turning fully counterclockwise, you eventually lose the signal, as you'd expect. Midway in the fine-tuning range, picture is fine (although monochrome) and audio is absent. Cranked all the way clockwise, you can just begin to receive audio, the picture is still fine, and there's still a monochrome picture.

It feels like the frequency center -- where color and audio pop in -- is just beyond that far range of the fine tuner. This is the same on every channel.

I'm used to tuners where you remove the knobs and adjust an individual oscillator slug (for the selected channel) through a little hole. This tuner appears to be built that way, but I'll be darned if I can find the magic hole. The manuals that I have don't mention the oscillator slugs except in the context of a full-bore tuner alignment, which I'm not equipped to do.

If I'm missing something obvious, or barking up the wrong tree, please tell me now :)

Phil Nelson

It may need an alignment of some degree. I stopped working on mine due to RF/IF/AGC intermittents, and more so the glaring issue that I could fine tune monochrome, color, and sound, but not more than one properly at the same time.

You may be right. I tried tweaking the sound IF to move it into the "good mono picture" zone. I had to crank the adjuster all the way to the end of its range to get an improvement.

Maybe I'll push this one back against the wall for now. If I want to collect the gear & expertise to do an alignment, I'd rather practice on a B/W that already works well, rather than this guy.

It's frustrating when the colors show up well in test patterns, but not otherwise.

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

http://antiqueradio.org/art/RCACTC-4RedPurity.jpg

http://antiqueradio.org/art/RCACTC-4BluePurity.jpg

http://antiqueradio.org/art/RCACTC-4GreenPurity.jpg

http://antiqueradio.org/art/RCACTC-4Convergence.jpg

http://antiqueradio.org/art/RCACTC-4ColorlessImage.jpg

You don't need a full alignment. You just have to find those magic
holes. My Sam's says they are there. You need not fear adjusting
just the oscillator frequencies ... its absolutely the easiest
thing to get set in the tuner.

I guess there is nothing to lose by trying to adjust the oscillator slugs. I will need to make a new tool. In the process of packing up & unpacking my workshop, I misplaced (!) my special screwdriver with a whittled-down handle. I have a big pile of plastic alignment tools, but none of them is right for this job.

Phil Nelson

Adjusting the oscillator doesn't seem to be the magic bullet. I made a tool and used a tiny penlight to confirm that there is an accessible slug at the end of the tunnel labeled 12. After a little turning, now I can break up the video and audio at either end of the fine tuning range for that channel. The audio is outstanding near the clockwise end of the range, just before the picture breaks up. Still no color where you'd expect it, though.

Phil Nelson

IIRC on mine there is a point where the monochrome is really sharp. On one side of that point mono is blurry, but the audio is really clear, and on the other side if tuned to the ragged edge of the mono, and after sound is lost color comes in....Granted on mine some clod knocked one of the IF cans off the video board and I had to cobble it back on so god only knows what that did to mines alignment.

It is frequently said that these old sets don't really need realignment.
I've found that untrue. All my sets ... Pilot TV37, RCA 9-T-249, Emerson 610
and RCA CT-100 had abysmal alignment. True, many of the very sharp
trap frequencies were spot on, but the overall IF shape was in
every case completely wrong. Many RF channels were off too.

Its a lot harder to recognize on a B&W set, especially a narrow band
one like the TV-37. My opinion is that the best test on a B&W set
is the standard 100% color bars pattern (WYCGMRB). If alignment is spot on
you should have no problems with the relative brightness of the
bars versus fine tuning as you tune so the video carrier rides up from the
1/2 point to the 100% point. If its off, you will notice
problems. You can use 75% bars but 100% is a much better test.
This is what I fought with a long time on my CT-100.

I don't really know about other chassis, except that most of my older sets look maybe just OK, but my CTC-4 luminance section probably couldn't be more "sharp", or provide a more excellent picture. Chroma is also very good, but narrow band, as most know. Perhaps just a lucky circumstance, or maybe an extra measure of diligence to provide decent pics to encourage sales.
My 4 also has a correct gamut CRT, before the "gray screen" tubes. Best viewed in a totally dark basement LOL. :yes:
Kevin

I don't really know about other chassis, except that most of my older sets look maybe just OK, but my CTC-4 luminance section probably couldn't be more "sharp", or provide a more excellent picture. Chroma is also very good, but narrow band, as most know. Perhaps just a lucky circumstance, or maybe an extra measure of diligence to provide decent pics to encourage sales.
My 4 also has a correct gamut CRT, before the "gray screen" tubes. Best viewed in a totally dark basement LOL. :yes:
Kevin

My CTC-4 produced one of the most detailed, sharpest monochrome pictures of any vintage set I've owned when fine tuned for best best monochrome picture...

Before I cry Uncle and throw a tarp over this TV, I scoped the input of the first video amp to see what is getting through the video IF section.

My pattern generator is set to color bars, which the TV displays as gray bars.

http://antiqueradio.org/art/RCACTC-4ColorlessBars.jpg

The top scope trace is the TV's video IF output. The bottom trace is direct from my pattern generator.

http://antiqueradio.org/art/RCACTC-4VideoIFOutput.jpg

The signal looks pretty scrawny by the time it gets through the video IF chain; the burst signal is basically missing in action. Tell me if I'm wrong, but I'm taking this as a sign that the TV really does need realignment.

Phil Nelson

Try injecting a composite signal to the 1st video amp, if you haven't already. That would eliminate the IF as a fault area. If that's not it, it's likely a mistuned trap somewhere.

Hmm, results inconclusive. I pulled the 3rd video IF tube and injected video from my little Leader pattern generator at the grid of the 1st video amp. The picture had extremely weak sync and it showed a faint image.

http://antiqueradio.org/art/RCACTC-4InjectingVideo.jpg

Then I looked at the CTC-4 schematic and noticed that the 1st video amp is expecting +2.7V on its grid. That pattern generator certainly doesn't provide a signal that strong.

I tried using my B&K TV analyst as the video source. Cranking its video output control to the max gave me something over 2V, but still not enough sync for a stable picture. Still no true color, either, but if the signal is too weak to pass a usable color burst, I'm not sure what that proves.

Phil Nelson

I think I left the IF tubes in when I did it, but it's been so long now I can't remember. You put the signal right in to pin 2 or the 6CL6 and chassis ground, right? If it's not getting a picture, you may have a bad AGC pot on your hands. Mine was completely trashed when I first got the set, wouldn't display much of anything. Check to make sure it's responding, then move on to scoping the signal you're injecting at the CRT cathodes. If it's not coming through, there's still some issue somewhere. My set definitely works when injecting composite.

Some vintage color TVs had a separate detector diode for the chroma, separate from the regular video detector. Your oscilloscope display of the luma video would be typical found at the regular video detector of such a set.

Some vintage color TVs had a separate detector diode for the chroma, separate from the regular video detector.Yes, that trace does look more like a luma-only stairstep pattern, but this set only has the one detector diode.

You put the signal right in to pin 2 or the 6CL6 and chassis ground, right?Yup, signal to pin 2 (or 9) of the 6CL6 and ground to chassis. I re-cleaned the AGC pot and made some cursory measurements that seem to indicate it's OK. Let's hope it is not junk. It is mounted concentric with the 2.5-meg noise threshold pot, and I don't know where you would get a replacement dual 500K/2.5-meg pot nowadays. Worst case, you could drill a new hole and mount a new pot separately, but . . . .

I put the chassis up on the workbench and plugged in the yoke & convergence assembly so that I can do some more systematic voltage & resistance checks, and look at things more easily with a scope.

Phil Nelson

I don't think the chroma could be completely missing, it's likely very attenuated after passing though the IF. I'd bet if you used the scope to zoom in on one of the luma bars, you'd still see a bit of 3.58 modulated on them. That's why there's a band pass amp, to bring the 3.58 back up to the point where it can be processed in the set. Same principle as attenuating sound before it messes with the video, then amplifying it in the audio section in intercarrier sets. Does your pattern gen have a means of switching off the chroma when bars are on screen? If so you can probe the band pass amp or demod driver to see if the chroma signal is getting though, switching chroma on and off while you probe gives you a way to make sure you're not just looking at noise. If it isn't getting through, you're probably looking at a slope adjustment to the IF at the very least because the 3.58 has likely slid off to one side and is not being seen by the set anymore. If the chroma is still there, it's likely the color AFC needs attention. You were able to get solid color raster before, but that is a very strong signal and is easy to lock onto. A weaker scene type signal might be throwing it off, so see if doing the zero-beat procedure does anything to improve it. I don't have many more ideas, besides a full on alignment. You could mail me your chassis I guess, I have the rig to do it...

a full on alignment. You could mail me your chassisHmm, that's a tempting offer.

Meanwhile, I am checking things around the 6U8 AGC/burst keyer.

Phil Nelson

Does your pattern gen have a means of switching off the chroma when bars are on screen? If so you can probe the band pass amp or demod driver to see if the chroma signal is getting though, switching chroma on and off while you probe gives you a way to make sure you're not just looking at noise. If it isn't getting through, you're probably looking at a slope adjustment to the IF at the very least because the 3.58 has likely slid off to one side and is not being seen by the set anymore.

This is it right here.... Replacing every cap means all tuned circuits need re-alignment.
Chances are each tuned circuit has moved it's center up or down, and as
a unit, is just rolling off before the chroma part and attenuating it..... Easy
fix, but yes be sure everything else is ok....

.

Squirrel boy, Most of the caps we replace in sets like this are not in the IF tuned circuits (including the odd paper or two in the IF section of some sets).

Does your pattern gen have a means of switching off the chroma when bars are on screen? If so you can probe the band pass amp or demod driver to see if the chroma signal is getting though, switching chroma on and off while you probe gives you a way to make sure you're not just looking at noise.Good idea. Yes, my generator has a Chroma Off switch, so that would be easy to do.

Gack. I was measuring something else when HV disappeared and the 6CB5 horizontal output tube began to red-plate :sigh:

I pulled the 6CB5 and it is toast. No spares for that in the house, so I'll have to order a replacement (or two, for good luck).

Meanwhile, I assume it's OK to power up the chassis on the workbench (with yoke and convergence coils connected) with that tube removed . . . .

Phil Nelson

I have begun to investigate the red-plating condition on the 6CB5 horizontal output tube. I pulled the HOT, VOT, and damper tubes in hopes that I can safely check voltages & waveforms. The yoke and convergence coils are connected.

The screen grid voltage (pin 1-8) on the HOT is MUCH too high, about double the expected voltage. The resistors between that point and the +350V supply (R140, R141) check out OK. (These are Sams numbers.) The cathode voltage (pin 3) is in the ballpark, measuring -25V where -23V is expected.

Moving back to the 6SN7 horizontal oscillator tube, its resistances look reasonable but its voltages are off. Instead of -85V at the grid (pin 4), I measure -1.5V. The expected waveform (W13) at point L is not correct. It is a muddy slope similar to W14 instead of the classic W13 waveform with the rounded shoulders and nice peaks that I saw the first time I powered up the TV:

http://antiqueradio.org/art/RCACTC-4FirstPower.jpg

The horizontal has always been rock-solid on this set, so it's disappointing to see it degrade. Subbing oscillator tubes had no effect on voltages or that waveform.

I hope I'm not barking up the wrong tree in checking these things. I hope even more that the flyback hasn't failed. Besides checking components around the oscillator, I'll see what I can learn by testing resistances on the flyback.

Phil Nelson

Here's the schematic showing the horizontal tubes mentioned in my last post.

Phil Nelson

http://antiqueradio.org/art/temp/RCACTC-4HorizSchematic.jpg

...I hope even more that the flyback hasn't failed. Besides checking components around the oscillator, I'll see what I can learn by testing resistances on the flyback.
Don't you have a B&K Analyst (or other source of horz grid drive)? If so, you could lift the 'upstream' end of C115 and inject there, just to verify everything downstream of that point is kopusetic.

Yes, I have a B&K Analyst 1077B that can produce a horizontal grid drive signal.

I assume you mean injecting that signal with the HOT and damper tubes back in place. I will keep a close eye on things and shut down immediately at any sign of trouble.

Phil Nelson

Here is the TV Analyst's horizontal grid drive signal. Very stable.

http://antiqueradio.org/art/RCACTC-4InjectingHorizontalDrive.jpg

I disconnected C115 at its junction with R138/R139 and injected the signal there. With tubes back in place, the screen grid voltage at pin 1-8 dropped from 350V+ to around 125V (160V expected) and the HOT did not red-plate. The voltage at grid pin 4-5 was -75V instead of the expected -38V.

Out of curiosity, I reconnected C115 and tried the set without the injected drive signal. The HOT red-plated and I shut down immediately.

Which suggests something fishy upstream of the HOT, I guess.

This was done on the workbench. I suppose I could set the chassis behind the cabinet and connect to the CRT with this setup, if it's important to look at the screen and judge whether the flyback is still alive. I don't have extension cables for the yoke/convergence/CRT, but the original cables reach if I put the chassis on a big box. It's just hard on the back to crouch down on the floor to measure things :)

Phil Nelson

I think you can safely presume the fly is OK and the problem lies entirely in the osc. area. I would concentrate on getting the osc running right as the first order of bizness.

I will check things around the oscillator tube. The tubular caps and resistors were eliminated long ago. That leaves a handful of mica caps + the various coils.

Phil Nelson

Resistors fail randomly sometimes, and a tiny percentage of new caps are bad shortly after failure....Don't discount all possibilities.

I like that you gave the pet shelter extra $ - man, that's such a clean looking tv. My wife is crazy about these older tvs, too. I'll have to show her this one. Like the rest here, I'm hoping for the best, even if you don't need yet another project.

Phil R.

Yay, the oscillator is oscillating again.

http://antiqueradio.org/art/RCACTC-4HorizontalSweepRestored.jpg

I replaced three mica caps and a couple more resistors in the horizontal AFC/osc circuit and my favorite waveform is back. Also HV (25KV) and a screen image. Two of those micas (C106, C110) were rated for 1KV, so I tend to point the finger at them, although I have no way to test a 1KV cap.

Which puts me back where I was a week ago, wanting to see some color in those dratted color bars. Before messing with color, though I'm going to behave responsibly for a change, and work through the procedures for HV adjustment and HV performance check. The manual says that involves measuring current at the 6BK4 regulator cathode as well as at the HV fuse.

Interestingly, when I put on a color bar pattern, I saw some rippling waves of color, rather than monochrome bars, and the Color and Hue controls actually had some effect on the image -- the first time ever.

That gives me hope of solving the color issue eventually. But first I need to do the HV adjustments and some other voltage checks, so I can play the set for more than 60 seconds without fearing a meltdown.

Thx again for the advice.

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

After a detour to restore yet another CTC-11 (which needed very little work), I'm preparing to tackle the color issue again. In the meantime I got a new pattern generator with variable chroma output, which should be ideal for following up on Nick's suggestion to vary the chroma while looking at a tube such as the chroma bandpass amp.

While I have the CTC-11 on the workbench, it seemed a good time to try this method and see what the results look like on a similar TV that displays color very well. Here's an animated GIF showing pin 1 of the CTC-11's chroma bandpass amp (6AU6A) at 0%, 50%, and 100% of chroma output from the generator:

http://antiqueradio.org/art/CTC-11ChromaBandpassAmpAnimation.gif

Pin 1 of the chroma phase detector (6AL5) also has a waveform that changes obviously in response to varying chroma input:

http://antiqueradio.org/art/CTC-11ChromaPhaseDetectorAnimation.gif

My idea is to get the CTC-4 back on the bench and scope the bandpass amp and phase detector and watch for change when I vary the generator's chroma output. I hope this will answer the question whether a usable color signal is making its way through the TV's video IF section.

We're leaving tonight for a mini-vacation, so I may not be able to try this until this weekend.

Phil Nelson

I think it is fair to say we are all pulling for you, learning from you and excited about this Phil!

Yes, I await the results of your always-informative tests and comments, Phil. Good luck with the set.

Back to the CTC-4. Here are comparisons of the signal at the video amp input. The first photo shows the CTC-11, which makes a nice picture with accurate colors. On the bottom is the video output direct from the generator. Above it is the output from the CTC-11's IF section, where it enters the video amp.

http://antiqueradio.org/art/RCACTC-11VideoAmpInput.jpg

The CTC-11 IF output isn't perfect, but it resembles the color-bar signal and it seems to have a healthy burst signal. My reason for looking at this is to understand what the video amp input should look like in a similar color TV that works normally.

Next is the CTC-4's IF output where it enters the video amp. Here, the direct color-bar signal from the generator is on the top and the CTC-4's signal is on the bottom.

http://antiqueradio.org/art/RCACTC-4VideoAmpPin9.jpg

The CTC-4 signal is attenuated, to say the least.

I have a bad socket on the IF board, the 3rd video IF amp. I have cleaned the devil out of that socket, swapped tubes, etc., but the socket is very intermittent. Only by nudging the tube into exactly the right position will it pass a signal at all. In the wrong position the screen goes completely dark.

I did scope some of the CTC-4's color tubes (chroma bandpass amp and chroma phase detector), but the photos aren't worth including. Those waveforms look like no usable color signal is present.

There's obviously something wrong with the IF socket, so I guess I'll address that, either by ordering a replacement socket or trying to transplant new pins into this one (a trick I haven't tried before).

Phil Nelson

Phil, your step-by-step analysis and documenting of the process are enjoyable and informative, as always. I wish I had something to add, but I can only think that it might be an IF alignment issue.

Another trick would be, inject a color baseband video signal into the stage where you are seeing the total lack of color signals/frequencies (the lower trace in your CTC-4 scope picture) and see if the rest of the set's color circuitry works OK. Then, inject the same signal but at IF, into the IF stages one by one backwards and see if you can narrow down where the problem starts. Suitable signals should be available from your B&K 1077, I think.

Thanks, I have tried injecting a video signal (color bars) at the input of the first video amp, without getting a coherent color image. I believe the TV expects a signal of about 2.7 volts there, but my generator can supply only 1.5 volts at most, so perhaps the signal is just too weak.

The RCA manual ( http://antiqueradio.org/art/RCA%20CTC-4%20Television%20Service%20Manual.pdf ) has an interesting section on pages 22-23, "AFC alignment used for chrominance circuit analysis." It explains how to remove the chroma bandpass tube and then measure voltages at the chroma phase detector, R-Y/G-Y demodulators, and 3.58-mc oscillator, to determine whether the 3.58-mc signal is present and traveling where it's supposed to go.

My set flunked all of those tests, so I am starting to wonder if it has more than one problem (wouldn't be the first time). For instance, maybe it has lousy video alignment AND the chroma reference oscillator is not running (or running at the wrong frequency).

I thought I had licked the IF socket problem. I gave all three sockets yet another military-grade cleaning and then resoldered the 3rd IF socket pins. This seemed to eliminate the intermittency, but after messing with various things for a couple of hours, the problem returned.

Tomorrow I'm going to complete the systematic voltage & resistance checks which I started a long time ago and never finished.

Phil Nelson

Might be time for new sockets. IIRC surplus sales of Nebraska had the correct sockets for these last time I checked (a good 3 years ago). I've been wanting to buy three new Video IF sockets for my CTC-4, but have yet to come up with a minimum order to merit purchasing them, and like you I've got alignment issues and lack the knowledge/equipment/time to do pick up the craft......After I graduate this year I hope to have sufficient free time and monies to gear up for TV alignment.

To give direct video input another shot, I disconnected the output from the video detector to the 1st video amp, and injected a video signal to the video amp grid. I started with a B/W crosshatch pattern so that I could adjust the screen background, etc., to make a normal display.

http://antiqueradio.org/art/RCACTC-4DirectVideoInput1.jpg

Then I switched to a color bar pattern.

http://antiqueradio.org/art/RCACTC-4DirectVideoInput2.jpg

Adjusting the Color control, etc., gives nothing like a normal color-bar progression, so I'll check out the color circuits.

Phil Nelson

That would appear to be a symptom of the chroma reference osc. not working properly.

Yes, that will be my first stop. The previous tests gave no evidence of the chroma oscillator working, and I just ran across this note in another part of the manual:

"If the 3.58 mc. subcarrier oscillator does not operate and provide adequate bias voltage to the grids of the G-Y and R-Y demodulators, a picture having an overall yellow-green cast will result." That just about describes that awful color-bar image.

I don't know if you can test a crystal with my feeble collection of instruments, but I have a handful of 3.58-mc crystals left over from previous adventures, so I can test by substitution if I have reason to suspect a bum crystal.

Phil Nelson

Why not just poke around in the chroma
of area with your scope?

See if the oscillator is oscillating. If so, then ...

Look for a burst at the output of the burst keyer.

Do note that the color won't sync unless the horizontal
is working correctly. I don't know if the color killer will kill the
color if the horizontal pulse driving it is not right. It doesn't
on my CT-100.

It seems that you already have scoped for seeing color subcarrier
somewhere in the video, and not seeing it. But was the horizontal output tube replaced by then? If not ... expect problems because the AGC won't work
without it. On my CT-100 the IF response becomes hopelessly narrow
and peaked in the middle
of the channel.

Thanks, I replaced the horizontal output tube right after I fixed the horiz oscillator.

Earlier today I started scoping things in the chroma circuits. Since it's doubtful whether the IF section is passing a color signal, I disconnected the output from the video detector and injected a video signal from the pattern generator at the video amp grid. With luck, I can get some clue whether the chroma circuits are operating.

The waveforms on the burst keyer tube look pretty normal. Here's the burst keyer grid (pin 9):

http://antiqueradio.org/art/temp/RCACTC-4BurstKeyerGrid.jpg

Here's the burst keyer plate (pin 1):

http://antiqueradio.org/art/temp/RCACTC-4BurstKeyerPlate.jpg

Here's the burst keyer cathode (pin 8):

http://antiqueradio.org/art/temp/RCACTC-4BurstKeyerCathode.jpg

http://antiqueradio.org/art/temp/RCACTC-4WaveformModels.jpg

I also scoped the bandpass amplifier, demodulator driver, color killer, blanking amp, and G-Y/R-Y demodulator:

http://antiqueradio.org/art/temp/RCACTC-4ChromaBandpassGrid.jpg
http://antiqueradio.org/art/temp/RCACTC-4DemodulatorDriverGrid.jpg
http://antiqueradio.org/art/temp/RCACTC-4ColorKillerGrid.jpg
http://antiqueradio.org/art/temp/RCACTC-4BlankingAmpGrid.jpg
http://antiqueradio.org/art/temp/RCACTC-4G-YDemodulatorGrid.jpg
http://antiqueradio.org/art/temp/RCACTC-4G-YDemodulatorOutput.jpg
http://antiqueradio.org/art/temp/RCACTC-4R-YDemodulatorGrid.jpg

I haven't pored over all this yet, but I get the idea that some of those circuits are operating, anyhow.

Phil Nelson

Phil,
Although I'm not overly familiar with sets earller than CTC-12, I'm assuming the following 'quick & dirty' check is valid for your CTC-4 as well:
While watching the colorbar display as shown in your post# 138, rotate the color control thru its full range, from zero to maximum, a few times. Does that greenish component vary in intensity, extinguishing completely at the zero setting? If so, it indicates the chroma signal amplitude is being displayed, but without the local phase reference signal. In other words, the 3.58 oscillator is not running.

Or not running at the correct frequency. The procedure for aligning the local oscillator is to ground the input to the reactance tube, then twiddle the slug of the oscillator till color bars slowly float by. If it won't even do that, it's not running and you can verify by loosely coupling a scope probe to the 3.58 tube's plate and look for a sine wave output.

I suspect the oscillator is simply not running. Trying old_coot88's test, when I turn down the color control, the color in the color bar pattern is totally extinguished.

When I check voltages on that tube (V124A, 6AZ8), the grid at pin 6 shows 0V instead of the expected -10V. I see no waveform at all when I put the scope probe at (or near) the plate, pin 1, as miniman82 suggested.

http://antiqueradio.org/art/temp/RCACTC-4ChromaOscillatorSchematic.jpg

The other voltages at that tube are in the right ballpark and the resistance at pin 6 is correct (47K).

I guess the obvious question is, why no negative voltage at pin 6?

The other check, watching for drifting color bars while you move the oscillator slug, is part of the color AFC alignment procedure that I mentioned earlier.

http://antiqueradio.org/art/temp/RCACTC-4ChromaOscillatorCheck.jpg

When I made this check, no drifting bars were visible, leading to the conclusion that the free running frequency of the oscillator is not correct.

Phil Nelson

Did you check the reactance coil itself for continuity, and +280V on the plate of the reactance tube?

(open reactance coils were pretty common on CTC-15 forward, dunno about CTC-4s.)

I measured about +270V on the plate (pin 6) of the reactance tube (V122B). The reactance coil L127 has continuity, measuring about 10 ohms resistance.

Phil Nelson

How about plate and screen grid voltages on the osc. tube? And continuity of the coil going to the cathode? If all good, maybe the xtal.

I measure +249V on pin 1 and +118V on pin 2 of V124A. Resistance from pin 3 to ground is zero, suggesting that coil L42 has continuity. Maybe I will dig out one of those spare crystals and try substituting it. They are all the plug-in type, so I'll need to solder on some little leads.

Phil Nelson

I suspect that the xtal substitution will answer the question, but then I was wrong before about your CT-100 xtal :scratch2:

Be careful soldering to the pins, heat sink them if you can.

jr

Well, I subbed two different 3.58-mc crystals and took care not to overheat their pins.

No change in symptoms. I'm still lacking the negative voltage on pin 6. Still seeing the greenish color bars that disappear when you turn the Color control down.

Seems unlikely that all three crystals would be bad, although I guess anything is possible.

Phil Nelson

I would check or replace C202,
Check or temp remove C209 - check for grid voltage change.
What resistance grid to ground...?
Check or replace C213.

In that little test, no color barbar-pole means no osc.
No -10v osc not running.

You probably have more than one problem looking at the low signal
quality of the burst way back many posts....

.

Replaced C202, C209, C213 -- no change. I even swapped 6AZ8 tubes out of superstition, but no go.

I know the video IF section is not great, so I disconnected that and injected video at the 1st video amp grid. Presumably that is a nice clean signal, although maybe not quite as strong as needed.

Phil Nelson

Replaced C202, C209, C213 -- no change. I even swapped 6AZ8 tubes out of superstition, but no go.

I know the video IF section is not great, so I disconnected that and injected video at the 1st video amp grid. Presumably that is a nice clean signal, although maybe not quite as strong as needed.

Phil Nelson

Are you sure that you have adjusted the fine tuning so that the video carrier is on the correct side of the if response? The consumer rf modulators are double side and the chromance could be lost if mistuned.

Does that make sense?

Terry

Yes, that makes sense. The tuner is not an issue right now, since I have disconnected the video IF section (and upstream of that, the tuner) to inject a video signal directly at the 1st video amplifier.

When I had things connected normally, I could observe differences when using the fine tuner to tune on either side of the "best" signal, but the TV never displayed anything resembling correct colors. I have done this with various sources -- DVD player, agile modulator, pattern generator, etc. The AGC and color killer appear to be working normally, too.

Phil Nelson

Getting the 3.58 osc running should be the #1 objective, irrespective of whatever other gremlins may still be lurking.

I'm open to suggestions about how to get that oscillator working. There aren't a lot of other components connected to that tube, other than a couple of ceramic caps and a few resistors.

Phil Nelson

I wonder if the capacitors in T115 could have gone bad ("silver mica disease" or similar)?

Or, if that transformer was sufficiently mistuned enough, would it kill the oscillator? Maybe, count turns (so you know where you started) and run its slug all the way from end to end and see what you get. I think if you got your scope connected to that circuit's output, you would see quite clearly if/when the oscillator started running.

Among the repairs I did on a CTC-4 several years ago, I replaced two 6AZ8s. You already tried that, though.

Here is a 'cover all your bases' suggestion: if you have a 9-pin 'socket-saver/extender' plug it in to the chroma osc. tube socket and see if you have continuity between it and the solder terminals of the socket. Every so often the metal in a socket contact will break in a spot that is hard or impossible to see.

Also if there is a shield on that tube try removing the shield, and seeing if there is an effect on trying to adjust the osc. I've got a CTC-15 that don't won't chroma synch and don't want to oscillate if the osc. shield is on and grounded...So I just removed the shield as a quick fix.

How about those resistors R248, 249, and 250???
R250 should be ok since you got your plate voltage....
Same with primary on T115.

Are the voltages on pin 2, and 3 correct....?

.

I'm open to suggestions about how to get that oscillator working. There aren't a lot of other components connected to that tube, other than a couple of ceramic caps and a few resistors.

Phil Nelson
Phil, I'm also fighting a chroma-AFC problem in a friend's CT-100. It exhibits a similar off-color operation. In my case the oscillator is functional and the CW to the demodulators is there and at the proper amplitude. And, as well as can be seen on a scope, the CW is in quadrature at the demodulators.

As has been suggested here with your problem, I will next concentrate on insuring the Reactance inductor and circuit are working properly.

Closed loops are tough cookies to crack at times!

Pete

if you have a 9-pin 'socket-saver/extender' plug it in to the chroma osc. tube socket and see if you have continuity between it and the solder terminals of the socket.Thanks, I did that very check yesterday afternoon. It occurred to me that I already had a socket issue on the video IF board, so why not check this one? This socket seems solid, knock on wood.

I will try to follow up on the other suggestions. It would be nice if I could just substitute a 3.58-mc signal, as you could do with a video or horizontal drive signal, but this situation does not seem that simple.

Phil Nelson

Why not try a 3.58 MHZ signal from a signal generator? disconnect the
crystal, feed the signal from the generator to the no-longer
oscillator's grid and look on the scope at the two outputs of the
output transformer. See what happens if you vary the frequency around
3.58 MHZ (on the scope).

Another thing is to check the crystal ... connect the sign generator
to it with a 10K resistor and look on the scope. You should see the
sharp resonance as you tune. Remember that a previous thread had
what was thought to be a bad crystal; they tried two good crystals and
they didn't work. It was a bad part. After replacing the bad part
but leaving in a "good" crystal it didn't work ... but with the original crystal did.
So these circuits are picky about the crystal. If the crystal is bad, it may
be that only an exact replacement will work.

Hey, I just remembered that my Sencore VA62A video analyzer can supply a 3.58-mc drive signal. I hauled it off the shelf and fired it up. My scope has a hard time locking on the signal, but there seems to be a waveform of sorts.

http://antiqueradio.org/art/SencoreVA62A3-58mcSignal.jpg

I disconnected the crystal and connected the analyzer's 3.58-mc drive output to pin 6 (grid) of the oscillator tube. After adjusting the generator's output voltage, I began to see rolling colors moving upward on the screen, similar to what I've seen before when the color sync was messed up on my CT-100.

http://antiqueradio.org/art/RCACTC-4RollingColorsAnimated.gif

I tried adjusting the reactance coil (L127 in the RCA manual) through its entire range, but this had no effect on the rolling, which never changed speed. And I still don't see normal colors, only rolling patterns against the same green-blue bar background. Turning the TV's Color control had the same effect as before: no change in the colors, and the image will just extinguish if you turn Color down far enough.

The symptoms are the same whether I send the color-bar signal from my pattern generator through the TV's tuner and (lousy) video IF sections, or inject video directly at the 1st video amp.

I'm going to go back and repeat the procedure outlined on page 22 of the RCA manual, disconnecting the bandpass amplifier, trying to adjust T115, and so on.

Phil Nelson

Its obviously best to use an accurate 3.58, but even the cheesiest signal generator will get close enough to test throughput ... just not phase.

Ignore the reactance tube for now, or at least keep the input grounded for the moment per the adjustment procedure so you can focus on getting the oscillator running. It's obvious you have no output from it, that's why you have zero grid volts on V124A and also sagging plate volts- that tube is probably turned on 100%. Make sure the .01uf caps to ground coming off pin 2 are not leaky (C2110/C211), then see if you can lift one of the primary winding wires of T115 (pin B or E) and measure resistance. It's possible your CW transformer has shorted or something, but tuned circuits can be deceptively hard to troubleshoot despite their apparent simplicity.

One last note: although the inductors in the CTC-4 chassis are not the dreaded white ones that always go bad like the CTC-2(B) chassis had, it's always possible you have a bad inductor still. Make sure L42 checks in at the proper resistance, and also ensure C209 isn't leaky.

Thanks, we hear and obey :)

Phil Nelson

There's also a couple of .001 caps (C219 and C220) across the secondaries of the CW xfmr. One of those could be wonky.

I believe C219 and C220 are inside the T115 can, but as chrisWA6TV mentioned, little micas inside xfmr cans have been known to go bad, especially the "naked" kind that are uninsulated mica sheets. I replaced some in the audio section of an Admiral set.

My back is just about played out for the day. Tomorrow I will grunt the chassis back onto the workbench and go on a cap-and-resistor hunting expedition.

miniman82 mentioned C209, which I already replaced, but that reminds me -- depending on what schematic I look at, that cap's value is given as 4, 4.7, or 6.8 pf. Here's the C209 that I removed:

http://antiqueradio.org/art/temp/RCACTC-4C209.jpg

I hate the codes on these little dogbone-shaped caps (and I have never found a bad one, but I replaced it anyway, while I was soldering on that terminal). What I had on hand was a 5 pf mica, so that's what I installed. I'm hoping that this code translates as 4.7 pf and that a difference of .3 pf doesn't matter here. If I'm wrong on one or both counts, someone tell me now, and I'll just put the old one back in.

Phil Nelson

P.S. The resistance across L42 is 10.6 ohms, which doesn't seem outlandish. The schematics don't give a resistance for it, only the notation 12 muh.

Check the CW trans, T115. It's a simple circuit, but the answer isn't always obvious.

P.S. The resistance across L42 is 10.6 ohms, which doesn't seem outlandish. The schematics don't give a resistance for it, only the notation 12 muh.
Back in post# 149 you wrote, Resistance from pin 3 to ground is zero, suggesting that L42 has continuity."
Since L42 goes to pin 3 (cathode), pin 3 should be showing 10.6 ohms to ground.
Were you measuring the coil with one end disconnected? If so, could there be a short inside the socket from pin 3 to ground?

Sorry, I've been flipping back & forth between the Sams & RCA schematics and jumbled some numbers.

The 10.8 ohms reading was across L127, the reactance coil. That is with everything connected on that coil.

Resistance from pin 3 to ground is 2.1 ohms. That's across L42 with everything connected. The RCA manual has no resistance chart, but for what it's worth, Sams says resistance at pin 3 should be .4 ohms, where I now measure 2.1 ohms.

I did some checking of T115, the CW transformer. Resistance across the primary (from B to E) is 7.0 ohms. Resistance from F to A (F to ground) is .1 ohms. Resistance from D to C (D to ground) is .1 ohms. This is with everything connected to T115.

Someone has worked in this area before. C202, the 120-pf cap on pin 6, looked like a replacement, attached hook-and-loop style to a stub left on the terminal. R246, 22K, is another obvious hook-and-loop replacement. The crystal may also have been replaced; one of its leads was much too long, and with strange bends -- not neatly dressed as you'd expect from the factory.

Phil Nelson

The schematic indicates there should be three ferrite slugs inside the CW xfmr. Are all 3 present and intact? No doubt they've been diddled with if somebody's been in there before.

Also, you stated R246 is 22K, where the schematic shows it as 2.2K.
Is the replacement red-red-orange (22K) or red-red-red (2.2K)?
In any case, that would not stop the oscillator from running.

You're right, it's 2.2K (red-red-red). When I lose the ability to read and type, that's a sign to break for the night :)

T115 has one adjuster slug accessible from the bottom and a second accessible from the top. The RCA manual says that the bottom adjuster is used in color AFC alignment and the top one for B-Y phasing. Both slugs are present and can be moved (the settings may be completely wrong, of course).

The Sams schematic seems to show that the two secondaries are adjustable, labeling them A64 (top) and A60. No label is given for the primary. I don't know why the primary is shown with an "adjustable" symbol if no adjuster is accessible.

Phil Nelson

Could it be a slug is missing from the primary? Or is there a big enuff hole to allow its exit?

(Edit) On second thought, it does look like an untuned primary, since there's no cap in parallel with it.

Only the secondaries are tuned, not sure why the schematic shows it is. Never caught that before, but it doesn't matter. Keep looking for bad parts, I'm sure you'll see something obvious sooner or later.

My guess is that the problem is in the cathode and grid area of the 3.58 MHz oscillator. If possible measure the component values, especially the cathode inductor L42 , its capacitor C213, the 4 pf feedback cap C209, the crystal and its resistor. Or maybe some conductive goo on the tube socket pins? My 21CT55 oscillator cathode tuned coil had been mis-adjusted and caused the oscillator to stop often.

I will keep plugging along. On the positive side, I tried dtvmcdonald's trick to test the crystals, and they all look good, including the one that was installed in the set. Each of them shows a distinct peak on the scope at around 3.58mc.

I replaced a couple more components around that tube, without making any improvement. This updated schematic shows the 5 caps and resistors replaced there.

http://antiqueradio.org/art/temp/RCACTC-4ChromaOscillatorSchematicUpdate.jpg

None of those components was grievously out of spec -- well, R249 measured 54K instead of 47K -- but at least I can cross those off the list of possible suspects.

Of the remaining components connected immediately to that tube, we also can eliminate the crystal, which tested OK, and resistor R248, which measures a hair over 47K.

Edit: I just saw the reply from Zenith6S321. One thing I haven't tried yet is disconnecting L42 to measure it. I can try that later on, along with giving the socket another good hard cleaning.

Phil Nelson

Why not try a 3.58 MHZ signal from a signal generator? disconnect the crystal, feed the signal from the generator to the no-longer oscillator's grid and look on the scope at the two outputs of the
output transformer.OK, I tried this (substituting the 3.58-mc signal from the VA62A analyzer at the grid of the chroma reference oscillator tube). It looks as if T115, the CW transformer, can pass the signal and be peaked.

http://antiqueradio.org/art/temp/RCACTC-4PeakingT115Animated.gif

In that photo, the scope was connected to terminal F on T115. By turning the bottom adjuster of T115, I could increase the amplitude up to a point, beyond which it fell off again. When I moved the probe to terminal D, the waveform looked about the same, although I didn't try the top adjuster.

None of which helps me figure out why the oscillator doesn't oscillate, but I'm taking it as evidence that T115 is operational, anyhow.

I had to move the adjuster quite a long way from its original position to find the peak, but perhaps that isn't surprising, given that many of the components attached to T115 have been replaced.

Phil Nelson

By sheer elimination, it begins to look like maybe the resonance point of the L42/C213 tank circuit is too far off from 3.58 to allow oscillation.

Do you have a signal genny that's reasonably well calibrated, and can be manually swept thru 3.58mc? If so, you might try sweeping the tank and watch for the resonant point on the scope.
(But first disconnect the tank from the tube cathode and C209. Connect the genny and scope to the top of the tank.)

My signal generator is a rotten old EICO 324. You can sweep it manually, but calibration is a laugh.

Those two components are small and rather buried.

http://antiqueradio.org/art/temp/RCACTC-4L42C213.jpg

Seems simpler just to replace L42 unless it is unobtanium.

Phil Nelson

Try sweeping the combination of L42 and the 270 pF in parallel with it.
It should be close to 3.58 MHz. You could try disconnecting the 270 pF
capacitor and connecting in a standard 365 pF variable, and
varying that to see if you can get oscillation.

Try sweeping the combination of L42 and the 270 pF in parallel with it.
That's what I meant by 'tank' - both coil and cap in parallel.
You could try disconnecting the 270 pF
capacitor and connecting in a standard 365 pF variable, and
varying that to see if you can get oscillation.
Ha. I was going to suggest that very thing, assuming he's got an old AM radio tuning condenser knocking around somewhere.

Kinda wonder if the coil could have some shorted turns in it, considering the uber-fine gauge wire it's wound with.

Here's another idea that's sort of a 'Hail Mary' gambit..
See if the osc. can be made to free-run on just the crystal. Disconnect the LC tank completely and replace it with a resistor (leaving feedback cap C209 in place). Try several values of resistor, from maybe 47 ohms thru 560 ohms or more.
If it'll start and run, that would pretty well confirm the fault lies with the LC combo.

I simulated the circuit. The cathode tank needs to resonate
a bit below 3.58 MHz. Apparently its doing some phase shifting.
It seems non critical, 2.5 to 3.2 seems to work.

It's difficult to sneak a soldering iron into the place where those two components connect to the tube, much less other tools. In the event that I fry or mangle L42 in the course of experiments, what's a good replacement -- something like this?

http://www.mouser.com/ProductDetail/JW-Miller/5800-120-RC/?qs=sGAEpiMZZMsg%252by3WlYCkU6mPiiSn88CctRRhUO5QN1 Y%3d

Phil Nelson

I would say go for it. The extreme disparity in DC resistance is no doubt due to its having a ferrite core vs. the original's air core (hence fewer turns of wire).

I disconnected C213 and L42 from the oscillator tube, and when I lifted up L42, it looked scorchy:

http://antiqueradio.org/art/RCACTC-4L42Original.jpg

There was a layer of melted varnish sticking it to the green wire below. (I scraped that off before taking the photo.) The coil is missing varnish in the area where they touched, and some of its wires look burned black. It has continuity, measuring 2.6 ohms resistance. Not having another coil to compare, I have no idea what that figure means; if it has shorted coils, I suppose it could show continuity but have the wrong inductance.

Try sweeping the combination of L42 and the 270 pF in parallel with it.

I tried doing this, with inconclusive results. I can see a waveform, and I can see the waveform change in the X dimension when I sweep the generator past 3.58 mc, but I don't see anything like a peak.

It's possible I had things set up wrong. What I did was to connect C213 and L42 in parallel (but disconnected from the tube). Then I connected the sig gen at one end of this pair and the scope at the other end. I slowly changed the frequency of the sig gen and watched for a peak of some kind. Again, with my crude old generator, it's not possible to s-l-o-w-l-y vary the frequency around that exact point, or even hold it precisely, except at whatever frequency it flops to when you let go of the knob.

Phil Nelson

:eek:Dang. That swatch of carbonization looks like it involved a half dozen turns or more. That could sure play hobb with the 'Q' factor as well as alter the inductance.

Re. the sweep test, what you'd wanta do is leave coil and cap in parallel, with the lower end grounded. Then connect both genny and scope to the top (with their cable shields grounded, of course).

A parallel-resonant LC tank (which this is) exhibits highest impedance at resonance, grounding out all other frequencies.
But a series-resonant tank (L and C in series) exhibits lowest impedance at resonance, making it useful as a wave trap to ground out an unwanted signal.

OK. I visited the local surplus store and found a couple of 12muh inductors in a bin. Later today I'll try the sweep test on old & new parts and see what transpires.

Phil Nelson

To get the sharpest blip, you'd probably wanta use a small coupling cap from the gen to the tank. Maybe 10 pf or so.

Is this what you're talking about -- 270pf cap in parallel with the inductor, and 10pf on the end?

http://antiqueradio.org/art/RCACTC-4ModelTankCircuit.jpg

Seems to do nothing around 3.58 mc, but when I went lower, I could get a waveform showing up between about 2.3 to 2.7 mc, peaking in amplitude around 2.55 mc.

http://antiqueradio.org/art/RCACTC-4TankWaveformAnimated.gif

Out of curiosity, I made another little circuit using the old L42 and two more caps (10 and 270 pf). The response was basically the same.

http://antiqueradio.org/art/RCACTC-4TestingL42Original.jpg

So, either the original L42 was good after all, or I still don't have things set up correctly. (Or it could be some evil combination of antique signal generator, middle-aged scope, and antique brain :) )

Meanwhile, I installed a new inductor in place of the old L42 in the TV and reconnected things to the oscillator tube. No change or improvement. Still seeing 0 volts at pin 6 of the oscillator.

Phil Nelson

some obvious stuff here, is the tube socket good (use a test socket to make sure the tube pins are connected to the circuit. Different tube used? correct tube used? just trying to cover the bases.

Here is a crazy thought what if there is a tin whisker or some such shorting the grid to ground forcing it to be 0V?

Is that a low capacitance scope probe? If not, it may be pulling the tank freq down too much. To minimize loading, you could add a small cap in series with the probe. Just a 'gimmick' consisting of a few inches of wire twisted together should do it.

If you need to raise the freq, try a lower value tank cap. Maybe 100 pf to start, and see which direction you have to go from there.

It is a plain old direct scope probe. I tried adding a 2 pf cap in series with the probe and didn't notice a significant change.

I tried substituting a 100 pf and a 82 pf cap for the 270 pf cap in the tank circuit on the workbench. 100 pf raised the peaking point somewhat, and 82 pf raised it up to roughly 3.5 mc. I substituted an 82 pf cap in the TV, and observed no change or improvement.

I don't see any whiskers or solder crumbs anywhere on the socket, which I have cleaned and re-cleaned. I have tested the socket with an adapter in place, and tried running the TV with the tube in an adapter, with and without the shield.

When I tested the old coil (L42) in a tank circuit on the workbench, it responded the same as a new one. Substituting a new coil for the old one in the TV gives me the same result.

I guess I can't rule out a socket defect such as a hidden carbon track caused by a past shorting incident. That is a hard thing to disprove without stripping everything off the socket, at which point you may as well simply replace it.

Phil Nelson

try another Xtal?

geez this is going to be great when you find it (trying for a positive spin).

sorry a little late to the party, but was the 270pf the orig cap in the circuit?

I have tried substituting crystals (and testing those crystals on the workbench). Also swapping among my four available 6AZ8 tubes.

The 270 pf cap is new. If you go back a page or two, you'll see that I already replaced most of the components in the oscillator circuit. Nothing left to replace in the immediate vicinity except R248, the 47K resistor, and I measure 47K resistance at pin 6, as per the resistance chart.

Yes, I'm looking forward to making this set work . . . someday. It's pretty interesting, so far. The CTC-4 is one of those stops on the road between the CT-100 and later RCA color sets that I've worked on. When it gets frustrating, I just work on something easier for a while. The TV will still be there waiting, next day -- or next month!

Phil Nelson

what I was getting at was did you confirm the cap value against the orig? for value that is, just in case the schematic is wrong.

It is a plain old direct scope probe. I tried adding a 2 pf cap in series with the probe and didn't notice a significant change.

I tried substituting a 100 pf and a 82 pf cap for the 270 pf cap in the tank circuit on the workbench. 100 pf raised the peaking point somewhat, and 82 pf raised it up to roughly 3.5 mc. I substituted an 82 pf cap in the TV, and observed no change or improvement.

I don't see any whiskers or solder crumbs anywhere on the socket, which I have cleaned and re-cleaned. I have tested the socket with an adapter in place, and tried running the TV with the tube in an adapter, with and without the shield.

When I tested the old coil (L42) in a tank circuit on the workbench, it responded the same as a new one. Substituting a new coil for the old one in the TV gives me the same result.

I guess I can't rule out a socket defect such as a hidden carbon track caused by a past shorting incident. That is a hard thing to disprove without stripping everything off the socket, at which point you may as well simply replace it.

Phil Nelson

You could always ohm out the grid pin with respect to ground and surrounding pins to look for abnormalities....

one more, confirm the heater voltage.

While you've got L42 disconnected, check socket lug#3 (cathode) to ground. It should show open circuit (infinite resistance on highest ohms scale).

The C213 that I removed was marked as 270 pf, a "postage stamp" type mica. I just checked the heater voltage; it's 6.32VAC at a line input of 117VAC. With everything disconnected from pin 3 of the oscillator tube, resistance from that pin to ground is infinite.

Since the schematics call for 270 pf, I removed the 82 pf cap (which didn't improve anything) and reinstalled a 270 pf for C213. While I was there, I also replaced R248, the 47K resistor. With everything reconnected, the TV behaves the same.

Phil Nelson

Well, to re-verify the following:
1). B+ is correct (at the jct. of R249/R250).
2). R250 is correct, 1K (brown-black-red).
3.) Plate voltage (pin 1) is considerably lower than spec, indicating the tube is overconducting from the no-bias condition.

The only remaining suspect preventing oscillation is the primary of the CW xfmr possibly having shorted turn(s). Can the xfmr be unmounted and opened to inspect the primary?

Based on similar previous threads: the crystal is always suspect unless
tried and working in an identical circuit. Known good crystals that were
not 100% identical replacements have been known to not work.

Here's another (way out:rolleyes:) idea, since Phil now has an extra 12uh coil, and assuming he has an old 10-365 pf tuning condenser. But first I'd like to run it by the collective wisdom of the group and see if it has any merit.

Cut the crystal and R248 out of circuit as shown, and replace them with a tank consisting of the 12uh coil and the tuning cap. Sweep the cap and see if it'll hit a resonant spot where the osc will start and run.
The xtal is primarily for freq stability, but the osc should free-run OK on the LC circuit (shouldn't it?):saywhat:

Well, to re-verify the following:
1). B+ is correct (at the jct. of R249/R250).
2). R250 is correct, 1K (brown-black-red).
3.) Plate voltage (pin 1) is considerably lower than spec, indicating the tube is overconducting from the no-bias condition.


1. Correct.
2. Correct.
3. Not sure what qualifies as "considerably lower." I'm on the road for a few days and away from my notes, but I believe I have measured anywhere from +249V to +270V at pin 1, maybe a little more.

When I get back (Thursday), I can try some more things, including substituting different crystals and going on a treasure hunt for an old variable tuning condenser.

Phil Nelson

The circuit should not run without a crystal. It is the tank circuit.

The circuit should not run without a crystal. It is the tank circuit.
Sorta what I figgered. Just wanted to toss the idea out there before nixing it.

Phil wrote,Not sure what qualifies as "considerably lower"....but I believe I have measured anywhere from +249V to +270V at pin 1, maybe a little more.
You indicated about 249V, which is down from the spec'd 280V, showing the tube is dropping about 30V across the 1K resistor (R250). That's .9 watt and the resistor would be running quite hot. If it is, you might want to sub a 2 watt resistor during the troubleshooting period.

Wow! You got an amazing deal on that. Welcome to the Director 21 owners club lol!

You indicated about 249V, which is down from the spec'd 280V, showing the tube is dropping about 30V across the 1K resistor (R250). That's .9 watt and the resistor would be running quite hot. If it is, you might want to sub a 2 watt resistor during the troubleshooting period.I just remeasured those voltages. Today I measure +267.5V at the junction of R249 and R250. I measure +255V at pin 1 of the oscillator tube. R250 seems to be holding up.

The Sams and RCA schematics give somewhat different voltages at various points. In Sams the voltage at junction of R249 and R250 is given as +270V. In RCA it is given at +285V. Both give a nominal line voltage of +117VAC and I set my variac at approximately that level, but it's not a laboratory grade instrument and I'm using a DMM.

The Sams and RCA schematics agree in showing a 5V drop across R250 (either 270-265 or 285-280). Today it looks like I am dropping 12.5V (267.5-255).

I remeasured voltage at pin 2. It is +107V (Sams calls for +85V and RCA calls for +110V).

While I was away, I ordered a couple of new 6AZ8 tubes and tried subbing them out of superstition. No change.

I also installed two very short leads, coming out from pin 6 of the oscillator tube and ground, that I can use to substitute crystals more easily. I swapped all four of my crystals with no change. Still measuring zero volts at pin 6.

I removed the can from T115 (the 3.58 mc CW transformer) to replace the two 1000pf caps, C219 and C220. Now that I look closely, it looks pretty toasty.

http://antiqueradio.org/art/RCACTC-4T115Exposed.jpg

The resistance on the primary should measure 6.8 ohms according to the Sams schematic. I measured it at 6.8 ohms. When the caps were off, I measured the other coils; both of them have continuity and they measure at .2 ohms. I just noticed that the Sams parts list has a note stating, "R-Y windings = .2 ohms."

I tried the TV again after those cap replacements and saw no change.

I'm not sure how much faith to put in those resistance measurements. I'd feel a lot better if these coils looked brand spanking new.

Phil Nelson

I have ordered a replacement for transformer T115. A while back (post #179), I did a test that seemed to show that T115 is at least partly functional, but I suspect that didn't tell the whole story, and those coils look they overheated in the past.

If the new transformer doesn't improve the situation, I'm not sure what else to try, except to replace the tube socket.

I wonder if there's a way to do a bench test of the old transformer after I take it out?

Phil Nelson

Does it work with the capacitor from the
previous stage and the two outputs of T115 disconnected?

I would suggest the next step after checking that is to use the new transformer plus a complete set of new parts, including tube and tube socket,
and build a breadboard of the whole thing leaving out the capacitor
that connects to the previous stage and leaving the two outputs of
T115 disconnected. Run it off any 250-300 v power supply.
There is no need for short leads in this circuit, leave them long.

You need to get that working and then transfer parts to the
main chassis. These oscillators can be picky.

Does it work with the capacitor from the
previous stage and the two outputs of T115 disconnected?Let's see if I follow what you're suggesting. Do you mean disconnecting C202 from pin 6 of the oscillator (V124A) and disconnecting the leads from terminals D and F of T115?

http://antiqueradio.org/art/temp/RCACTC-4ChromaOscillatorSchematic.jpg

And then I put the scope on terminal D or F to look for a signal at those points?

Phil Nelson

The new part arrived (the extra can is from my TV).

http://antiqueradio.org/art/RCACTC-4NewQuadratureTransformerT115.jpg

The RCA part number is 100430 and the Meissner part number is 17-6014. I got this from Play Things of Past (http://oldradioparts.com/). I also checked with Moyer (http://www.moyerelectronics.com/default.aspx); they don't have the Meissner part but they do have a Miller 6025, which is equivalent according to their records.

I'm leaving tomorrow morning for another short trip, so I probably won't have time to play with this until next week.

Perhaps breadboarding this circuit is not a bad idea. In different schematics, the value of L42 is given as either 11 or 12 muh, and the value of C209 is given as 4, 4.7, or 6.8 pf. I believe I have all the needed parts on hand, except for a ready-made power supply. Maybe I can pull out the power/audio chassis from my Admiral 24C15 B/W set and tap that for B+ and filament voltage.

Phil Nelson

Before doing an external breadboarding, I would maybe try this first.. go ahead and mount the new can and hook up the primary (terms. B & E). Leave the secondaries completely unconnected to minimize loading.
Bring the scope probe close to either L42 or term. B to look for the osc signal.

It's amazing that part was still available.

Hmmm. I looked inside the can of the new transformer and discovered a resistor (looks like blue-gray-brown, 680 ohms) in parallel with each cap on the secondary coils:

http://antiqueradio.org/art/Meissner17-6014Internal.jpg

The data sheet also shows these resistors:

http://antiqueradio.org/art/Meissner17-6014QuadratureTransformerSchematic.jpg

Their "typical" circuit is different than the CTC-4, with a 6AN8 quadrature amp between the reference oscillator and the transformer. It looks like the circuit from the RCA CTC-2B; this schematic specifies the resistors as 680 ohms and the caps as 1500 pf:

http://antiqueradio.org/art/RCACTC-2BChromaRefSchematic.jpg

The labeling of the secondary terminals is a little different and the resistances differ from the original. I measure 1.7 ohms across the primary (B-E) and .3 ohms across each secondary (F-D and A-C). The original measures 6.8 ohms on the primary and .2 ohms on each secondary.

The question is whether this is a good replacement for the CTC-4. I suppose I could just stick it in (noting the labeling differences on the secondaries) and try old_coot88's most recent suggestion . . . .

Phil Nelson

Ain't those caps plactic molded paper type?

They look like good old-fashioned "postage stamp" style micas to me. The little resistor is tucked under the cap.

Phil Nelson

I had the same concern as Tom when I saw the size of the cap. Are you sure it isn't a molded paper type?

http://i157.photobucket.com/albums/t61/OZ132HOME/MicamoldCapAd.jpg

I hate these danged dot schemes, but according to this cheat sheet, the upper right (in that photo) dot would be silver if it's molded paper; a white dot indicates mica:

http://www.tpub.com/neets/book2/3g.htm

As for the rest, brown-green-red means 1500, silver means 10% tolerance, and the last brown means who knows what.

There's a little point on the green dot showing which direction to read.

The caps are stamped El-Menco on the back, which tells me nothing, since E-M made all sorts of caps, including mica and molded paper.

Phil Nelson

I could swear I've seen some domino cap charts that list white as paper...
The physical size, look and value (.0015uF) all scream paper cap to me.

I disconnected one lead of the cap for testing.

http://antiqueradio.org/art/Meissner17-6014_C290Disconnected.jpg

It's a little hard to see in the glare, but the eye tube's shadow is fully open, showing no leakage under 450 volts, using a new 1500-pf mica as a comparator.

http://antiqueradio.org/art/Meissner17-6014_C290TestsOK.jpg

I guess I will call this cap C290 after the CTC-2B schematic. Whatever it's made of, I'm calling it good enough for this application.

Now the trick will be to install it without torching everything else in the neighborhood, including parts I previously replaced.

http://antiqueradio.org/art/RCACTC-4T115Underside.jpg

Maybe I will install all new components and leads on the transformer first, slip the pre-wired assembly through the hole, and then connect up.

Phil Nelson

wow some of that lead dress looks really tight, with crossing paths.
I keep hoping to open this thread and see a big SOLVED beginning.

I disconnected one lead of the cap for testing.




http://antiqueradio.org/art/Meissner17-6014_C290TestsOK.jpg

Whatever it's made of, I'm calling it good enough for this application.


Phil Nelson

Definitely a mica - either silvered or mica foil. White is always Mica using the EIA code. I had to learn both the EIA and military (MIL-C-39) code.

Cheers,

Mica or Paper issue aside... Is that even the correct transformer... looks like it is configured the same as L-45, the quadrature transformer in the CT 100. Might be good to "breadboard" the circuit first to see if it will indeed oscillate without the buffer amp. :scratch2:

jr

Yes, that was my question -- should this xfmr work at all, given its component differences and the circuit differences between the earlier sets and the CTC-4? (The CT-100 has the same circuitry shown in the CTC-2B snippet I included a few posts ago.)

I sent a follow-up email to Moyer asking if they happen to have a data sheet for the Miller 6025 xfmr, which purported to be a match. They emailed me a scan of the data sheet, showing that the Miller xfmr is a match for the Meissner part -- not the CTC-4.

One way or another, I guess I'm destined to take the old transformer out. If breadboarding the new one doesn't work, then the last resort may be trying to rewind the original. But I could try the original in the breadboard circuit before attempting a rewind.

I have these parts on hand. Is this what we're talking about building?

http://antiqueradio.org/art/RCACTC-4ChromaRefOscBreadboardCircuit.jpg

I'm hoping I can tap the 6.3VAC filament supply and B+ supply from the power/audio chassis of my Admiral 24C15 B/W set.

Phil Nelson

Phil, there's something I was gonna suggest earlier to see if the osc can be coaxed to run, but thought the better of it until seeing the CTC-2 schematic. The CTC-2 has the osc plate clamped hard with a .01 cap.
Try disconnecting the CW xfmr's primary completely, and shunt directly across where the primary was. Bypass cap C211 is now clamped directly to the plate. This duplicates how the CTC-2 osc plate is wired.
Bring the scope probe next to L42 to see if the osc is running.
--
If not, maybe try a few higher values for R250 up to 39K to see if it makes any difference.
--
If still no go, maybe there's a conductive track inside the tube socket itself. Most likely lugs 3 and 6 (cathode and G1). If you disconnect those two lugs (no tube in socket), they should show infinite resistance to ground, verifying no conductive path.
Then (with lugs 3 and 6 still floating) power up and see that there's no positive voltage on them, verifying no leakage path from G2 or plate lugs.

If the socket shows good, I dunno what else would be revealed by breadboarding. But what the heck...

Try disconnecting the CW xfmr's primary completely, and shunt directly across where the primary was.You mean, disconnect terminals B and E, and then connect junction of C211/R250 to pin 1, right?

If you disconnect those two lugs (no tube in socket)Again, you mean to disconnect everything from pins 3 and 6, right?

Phil Nelson

maybe I am missing something here but is that just a amplifier that is tuned for the horz rate? maybe the issue is the tube before it? I see a cap coupling a signal to the control grid, does not look like a correction voltage but more like the signal to drive the tube.

You mean, disconnect terminals B and E, and then connect junction of C211/R250 to pin 1, right?
Yes.
--
Again, you mean to disconnect everything from pins 3 and 6, right?
Correct.

maybe I am missing something here but is that just a amplifier that is tuned for the horz rate? maybe the issue is the tube before it? I see a cap coupling a signal to the control grid, does not look like a correction voltage but more like the signal to drive the tube.
Which print are you referring to here?

You mean, disconnect terminals B and E, and then connect junction of C211/R250 to pin 1, right?Okay, with that lash-up, I see a regular waveform at L42 (pin 3 of the oscillator). This is with no signal to the receiver and a high sweep rate.

http://antiqueradio.org/art/RCACTC-4T115PrimaryDisconnected.jpg

If I supply a color bar signal at the video amp and slow down the sweep rate, I see a more complex waveform; the amplitude of this one goes down if I turn down the Color control.

http://antiqueradio.org/art/RCACTC-4T115PrimaryDisconnectedWithSignal.jpg

Not sure if the second trace proves anything, but it was interesting to look at.

Incidentally, with nothing connected to the primary (terminals B-E), it still measures 6.8 ohms as given in the Sams manual.

Phil Nelson

Okay, with that lash-up, I see a regular waveform at L42 (pin 3 of the oscillator). This is with no signal to the receiver and a high sweep rate.

http://antiqueradio.org/art/RCACTC-4T115PrimaryDisconnected.jpg


Yowie zowie! :banana:What's the actual p-p amplitude of that?
Looks like the thing is actually running.
OK (assumimg you haven't unmounted the old CW xfmr yet), just take the new one and connect its primary in place of the old one, using a couple of short leads (after removing that jumper). See if the osc still runs.

Maybe this photo will give a better idea what I'm seeing. My scope has a lot of trouble locking onto the signal -- hope it's not a phantom.

http://antiqueradio.org/art/RCACTC-4T115PrimaryDisconnecteda.jpg

Edit: I just connected the primary of the new transformer in place of the old one (i.e., B connected to pin 1 and E connected to junction of R250/CC211. I get the same waveform, whose amplitude collapses if I temporarily disconnect the primary.

Phil Nelson

...I just connected the primary of the new transformer in place of the old one (i.e., B connected to pin 1 and E connected to junction of R250/CC211. I get the same waveform, whose amplitude collapses if I temporarily disconnect the primary.
OK. Now reconnect the old CW xfmr's primary. Does it kill the osc? If so, this proves the old xfmr is at fault.
-
But the question remains, with the new xfmr's differences, will it deliver correct phasing, amplitude etc downstream?
-
Also, is the osc running with the new L42 or the old one?

Do you have a frequency counter or digital SW receiver to check the frequency? looks like it is running close to 5MHz, if your 'scope is in the calibrated position.

jr

Let's try this again. The scope is on channel B with the vertical set at 2 volts/cm. The sweep time is set at .5 us/calibrate, and I pulled out the 5x mag knob.

http://antiqueradio.org/art/RCACTC-4T115NewPrimaryConnected.jpg

I scrounged up my digital SW receiver and got a nice clear tone at 3586 kilohertz when I held the antenna near L42. The tone disappeared when I turned off the TV. I do have a frequency counter somewhere out in the garage, but I don't trust its accuracy more than the digital radio.

The oscillator is running with the new L42. It's running with new everything, except for the tube socket and the quadrature transformer.

If the oscillator is indeed running, that feels like progress. Time to call it a night; I can try some more things tomorrow.

Phil Nelson

I'd say the tube socket is fine, provided there's no intermittency when you wiggle the tube.
-
If you end up using the new CW xfmr, it'd be a good idea to clip out those two resistors before installing it. That way, if the resistors are actually needed, they can be placed externally.
-
If it's the primary bad in the old xfmr, it may be re-windable using roughly the same gauge wire and same number of turns.
The primary is untuned, serving only as coupler or 'tickler' to the secondaries, so its exact inductance is not critical.

When I reconnect the old quadrature transformer (still in place and connected to everything else), the 3.58-mc waveform is visible and I hear a tone WHEN there is no signal to the receiver.

http://antiqueradio.org/art/RCACTC-4OscillatorWithNoSignal.jpg

When I turn on the color bar generator to inject a signal at the 1st video amp, the waveform is flatlined.

http://antiqueradio.org/art/RCACTC-4OscillatorWithSignal.jpg

I guess the oscillator is capable of running, but something else is killing (or swamping out?) the oscillation when a video signal is present.

For what it's worth, I reviewed my notes of voltage readings in the color circuits. I found wrong voltages on the grids (pins 2 and 7) of V125, the 12BH7, R-Y/G-Y demodulator tube, measuring near zero when those grids should have around -20V (or around -15V according to Sams). At the time I attributed this to the oscillator not running, since the outputs of T115 connect to those grids, but who knows?

Another anomaly at V121B, the 6AZ8 bandpass amp, where the grid should have about -12V and I measured only about -3V or less.

I haven't forgotten the toasted appearance of the old transformer.

Phil Nelson

:saywhat:So the osc runs now with the old T115 in place but wouldn't before.:headscrat What happens if you disconnect C202 (thus severing the osc from everything 'upstream')? Does it still run? If so, is there any sign of color barberpoling when you inject signal?

I disconnected C202. The waveform and tone are still present when there is no signal at the receiver. When I turn on the color bar generator, I see strong barberpoling on the screen.

Phil Nelson

burst keyer not working right?

Related to the burst keyer, I never got as far as trying the AFC adjustment procedure listed on page 23 of the RCA service clinic manual (specifically, adjusting T112, the phase detector transformer, or R228, the AFC balance control, which affect the keyer output). Pages 46-48 have more info.

Is it OK to use my digital multimeter for voltage measurements in those procedures, or will it load down the circuits too much? I don't have much faith in my old RCA Voltohmyst, but I could try using the scope for voltage measurements instead.

Phil Nelson

Wonder if you coulda cleared a tin whisker or something in the old T115 whilst removing and reinstalling it.:scratch2:
Now that you got barberpoling, try reconnecting C202, and go back further and disconnect R242. If still barberpoling, you should be able to zero beat the osc using the reactance coil, though it won't have any sync.

(Digital meters supposedly are high impedance like a VTVM, so shouldn't cause any loading problem.)

I would be tempted to scope and look for clean burst to be coming from the keyer. It like the osc free runs, but adding the control kills it, so maybe the control is not really a nice clean burst, but some video getting in there.

I reconnected C202 and disconnected R242. With no signal at the receiver, the waveform at L42 looks like the following and I hear buzzing instead of a clear tone from my SW radio tuned to 3586 KHz:

http://antiqueradio.org/art/RCACTC-4R242DisconnectedNoSignal.jpg

When I turn on the color bar generator, the waveform changes to this, and I see the same old green bars on the screen (no barberpoling). Louder buzzing from the SW radio:

http://antiqueradio.org/art/RCACTC-4R242DisconnectedWithSignal.jpg

I would be tempted to scope and look for clean burst to be coming from the keyer. It like the osc free runs, but adding the control kills it, so maybe the control is not really a nice clean burst, but some video getting in there.

If you scroll back to post #142, you can see three scope waveforms from the burst keyer. The first two looked good, the third (cathode) not so much. I can repeat those now, if that's interesting.

Edit: Well, I'll be hornswoggled. I reconnected both C202 and R242 in preparation for scoping the burst keyer. (Everything is now reconnected, in other words.) To my surprise, I saw rolling color bars, which I can make to hover in place by adjusting the reactance coil (L127).

http://antiqueradio.org/art/RCACTC-4HoveringColorBars.jpg

??

Phil Nelson

Dang, it's almost as if a B+ line is not being bypassed adequately and has got a bunch of junk riding on it. Try scoping some B+ points and see if there's any unusual stuff on it (other than normal low level power supply ripple).

Not sure if I'm doing this right, but here is the +285V line at the junction of R249/R250 near the 3.58 oscillator tube, with no signal at the receiver:

http://antiqueradio.org/art/RCACTC-4285VBPlusNoSignal.jpg

When I turn on the color bar generator, the trace changes to this:

http://antiqueradio.org/art/RCACTC-4285VBPlusWithSignal.jpg

The traces are somewhat cleaner than what appears in the photos; both of them bounce up and down a bit on my scope.

I got similar results when scoping that line at its origin (junction of R266/C117B in the p-s) and at pin 2 of V117, the horizontal oscillator.

Phil Nelson

C201, .1uf good?

Do you mean C204 (on the RCA schematic)? That was replaced, but I can check it, just in case.

Phil Nelson