Looks like it will produce 20 kV. :thmbsp: The HV regulator is working, too. I can reduce the HV down to about 18.5 kV and up to 20 kV. When everything is working, I imagine I'll have to run it around 19 - 19.5 kV, just to have some headroom to maintain proper regulation.

I had also been thinking that if necessary I could try to add some turns back on the flyback. I won't be using the wire I removed, however, as you can see in the first attached photo. I didn't disassemble the flyback, but left everything enclosed in the core and frame while I unwound the coil. This meant that every few turns I had to cut the wire, to avoid having to pull a lot of wire through the opening. The insulation generally was destroyed as I unwound the coil anyway, so no use thinking about salvaging the old wire. Some new wire could be added with some kind of plastic mandrel walls to make winding reasonably straightforward. However, it looks like I may not need to do that.

The last picture shows a closeup of the flyback in the set. I coated the outside of the coil with some red insulating varnish. I may beef that up with something more at some point. I didn't want to glop too much on there yet in case I needed to add more windings.

As you can see, the focus rectifier is still not connected. Now I need to deal with the vertical dynamic convergence transformer issue and other things.

FYI: With the focus rectifier operating normally and with a low-contrast image, my CTC2 will crank out 22 kV; I set the HV 2 kV below that, and overall operation is satisfactory.

Pete

Tom that's a pretty good job, I would have done that too.... I think that if you keep the hv too high, it will draw extra current on the primary... What do you guys think....

Congratulations on a really delicate difficult operation on the flyback. Sounds like another historic CT100 is well on its way to being saved. Hope it all works out well.

Tom-

I am very happy to see your progress on the flyback problem, and I look forward to further news as you continue the project. Nice work!

I haven't had too much time to work on the set further this weekend, but I do have a vague semblance of a picture on the screen tonight.

http://www.videokarma.org/attachment...1&d=1384763635

As you can see, the red isn't very strong, but it is functioning. From the picture here, one might get the impression there is no red at all.

I'm not out of the woods yet by any means on the flyback. What I find is that with any significant brightness on the screen, the HV collapses down to 16 kV, and even lower at full brightness. So I'm definitely short a bunch of turns on the flyback. Focus is also very unstable, and I had to modify the range of the focus control to get even close to focusing properly.

I'll work on some other aspects of the set for a while, and then return to the HV problem. I may try adding more turns to the flyback, or try the voltage tripler module I have in another set (and run it off the primary of the flyback as was suggested back on page 1).

I have the vertical dynamic convergence transformer out of circuit now so I can apply the focus voltage. New transformer has been ordered from our fine colleague John Folsom.

CT-100 Focus control
 

I am not sure if anyone is aware of this but there is a Series of Tektronix tube type scopes from the 50's era that used an almost identical Focus control assy ( I can't exactly remember if it were focus but for sure a control in the HV area) it was a VERY large Scope, as a matter a fact I sold it to someone a couple of years ago for their CT-100 and it worked fine, the actual value was a small amount off but very close to the ct-100, the physical size and everything was identical, I had removed this myself from the older tube type scope for parts, the only part number on the control itself was 01080100., I remember the HV section of the scope had solder in small tube rectifiers, but its been a few years so I do not know the Model number.
I know the Focus and conv controls are impossible to find for the CT100
just passing this on from my experience on the CT-100

Fortunately my focus and convergence potentiometers are OK, but I imagine others who are not so lucky will appreciate knowing there is a possible source for replacement pots.

Gentlemen,

I have a pretty nice black and white picture on the set now (with sufficient red gun contribution as well). Color circuitry not working at all, but we'll get to that later.

What I'm having trouble with right now is focus stability.

I modified the HV regulator circuit to regulate well at a lower voltage for the time being, since my HV supply is a bit low. That allows the HV to be stable and well regulated at around 15 kV.

However, the focus is still not stable at all, and varies wildly (from nice and sharp to so badly out of focus you can't see anything). Probing the focus voltage, I see that it is moving around quite a bit (easily a factor of 2 with scene changes). Convergence transformer is out of circuit, so it is not the problem.

That got me wondering about whether the focus control was in fact correct. I had noticed when I got the set, that a previous tech had added extra resistors both above and below the focus control, which I thought peculiar. Measuring the resistance of the focus control I find it is only 1 M instead of the 5 M called for in both the Sams and RCA schematics.

Then I checked the DC convergence control and find it is only 10 M instead of the 15 M called for in the schematics.

Can you take a look at the attached pictures (first three) and let me know whether the controls look original? Or were they both replaced at some point by a tech that took the time to get shafts of the right length with no evidence of cutting, etc.? Maybe he couldn't get the right values.

Much to my surprise I found in my junk box a NOS 15 M "high voltage" control, IRC type HV-15 (last two pictures). Always wondered what that would ever be good for. I may swap that in for the convergence control (although the 10 M in there seems to work fairly well).

What I'm really curious about is why my focus is all over the place. With the 1 M control in there, the load on the focus rectifier is a bit lower resistance than it should be -- 11 M versus 13 M (I have added 2 M above the focus control to get a usable range, so only 2 M missing overall from the chain). That doesn't really seem like enough to really make such a big difference. Obviously the focus range adjustment is much smaller than it is supposed to be, but that wouldn't appear to explain the instability.

Would having a low second anode voltage somehow cause the CRT itself to draw more current on the the focus electrodes and overload my focus supply, in a manner that appears to be scene dependent?

It also seems to like to focus with a fairly low focus voltage -- more like 1-2 kV instead of the 3-4 kV in the schematic.

The 1X2 tests good, and I've also swapped it for an NOS tube, so I don't think that's the problem.

Not quite sure what's happening here.

Those look (superficially) the same as the pots in my CT-100. I found a couple of old photos that may be helpful.

http://antiqueradio.org/art/temp/RCA...VCagePots1.jpg
http://antiqueradio.org/art/temp/RCA...VCagePots2.jpg

Whether mine are original, who's to say, although I have no reason to think that they are replacements.

Nice progress on this set, by the way. You work about 100 times faster than I do.

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

Tom, have you replaced the focus filter capacitor? The one on the wiper of the focus pot.

Yes, I replaced that with .01 uF 6000 VDC capacitor from ASC.

Re. the erratic focus, is there any chance there could be an open condition in the CRT socket, either on the lead going to the focus anode or the conv. anode?

The convergence pin showed a lot of white corrosion, which looked like evidence of poor contact in the past. So I shined that one up. I also tightened all the socket pins, since I have intermittent contact on the filament. Much better, but still fails to have proper contact on the filament once in a while when I first put the socket back on the CRT after working on the chassis. The focus pin doesn't look bad, but that in itself doesn't really mean anything. The convergence pin seems to be working, since the convergence control has a big effect on convergence, and the convergence is stable once set.

I do wonder a bit whether the focus pin is making poor contact. The way the socket is designed, it's a little tricky to get a wire in there to wrap around the CRT pin as an independent method to see if the voltage is really getting to the pin. Sounds like I should probably put some effort into that. Or, if you have any particular suggestion how to go after that possible problem, let me know.

I would use an ohmeter on RX1 to verify solid continuity up thru the focus lead to the socket lug. If good, then maybe re-flow the CRT pin (is it pin 6?).

I've learned quite a bit more about what's going on with the unstable focus, and I suspect all of this is related to the flyback being different than the set was designed around (fewer turns on HV winding).

I checked out the connections from the focus supply through the potentiometer and all the way to the CRT pin 6. All looks OK.

Observing the behavior, it was clear that the focus voltage was varying a lot with picture brightness. A little more observation revealed that the focus rectifier filament was rather dim since I had modified the HV regulator to bring the voltage down to 15 kV (which I had done hoping to improve HV stability with too little voltage coming from the flyback).

Right away I was able to observe that by increasing the HV, the focus rectifier would glow much more brightly. In other words, loading down the flyback by regulating the HV down also knocked down the focus filament current a lot. With too little current, the focus supply had too little current to remain stable with changing current draw by the CRT focus electrode.

On the other hand, if the HV regulator was set too high, so that it was basically allowing the HV to be unregulated, there was an equally interesting effect. Now, the filament of the focus rectifier would increase and decrease in brightness along with changes in the scene brightness. In other words, a varying load on the HV also caused focus instability.

It looks like the regulation has to be just right -- low enough to keep a constant load on the flyback with changing scene brightness, but not so low that the flyback is overloaded and the focus rectifier filament runs with too low current.

At the moment, I can't really find a sweet spot where the focus is totally stable, but it is far better than before. It's also a question of how much brightness and contrast this set is really designed to deliver. With relatively low contrast, I could probably get things stable.

Or quite possibly, with a proper flyback, everything would work much better. I'll give some thought to either adding more turns to the HV winding (which will be a bit of a project, requiring much more disassembly and modification of the flyback than I did before), or seeing if a voltage tripler in place of using the HV winding can work.

So far, this is all very educational as far as the HV system of the CT-100 goes!

Tom:

Very interesting analysis. One thing I discovered when I restored my set is the HV/Focus is a marginal design even with an original flyback. High brightness/contrast scenes can regularly cause the regulation to fail and focus to go out. At first I thought it was just my set but this was then confirmed by other owners to be normal. In order to provide a stable picture, the contrast and brightness need to be set lower than we are used to in modern sets. I do find it hard to believe that this is the way these sets were designed but it seems so.

It would be interesting to hear what everyone who has a working CT-100 is seeing for focus stability, brightness, and contrast. Mine is almost acceptable now that I've backed off the contrast, and set the HV regulation to around 18 kV.

What it cannot handle well at all right now is a white screen. Quite a few commercials these days include a white screen with some text and a small picture. When a scene like that comes along, I get total focus collapse, with the screen practically going blank in a cloud of fog. Almost all other "normal" scenes are OK.

I'll probably leave it like this for a while and take some time to work on the color circuitry, and come back to the flyback / HV issues later.

Tim is correct. "blooming" is common on CT-100's when large bright/white images appear on the screen. This due to the design of the HV regulation circuits. Keeping the brightness/contrast at their minimums while maintaining a viewable picture helps. The focus on my CT-100 does tend to jump in & out but is unrelated to the HV design. I believe I have a bad focus pot. Current back problems prevent me from pulling the chassis to confirm.:nono:

-Steve D.

Maybe the marginal 'stiffness' of the HV/focus supply is just part of the charm and challenge of using the set. Maybe sorta akin to using an early radio.

I haven't noticed any of the symptoms being discussed, though I'm lucky to have a tube with perfect emissions on all three guns so it's pretty easy to get a bright image without taxing the HV supply.

http://videokarma.org/attachment.php...6&d=1334520695


Again, it's important to set up the horizontal and HV regulation circuits correctly. When doing a set, I always test the HV unloaded with the regulator disconnected to see where it tops out. My CTC-2 makes about 22.5kv, so I know it will easily make a stable 20kv with the regulator tube doing its thing. Other sets are not as good, my Wingate struggles to make 22.5 with no image on the screen and the regulator cap off. My CTC-4 on the other hand is absolutely leathal, I'm not sure where it topped out at since it overloaded my probe but WAG is around 38-40kv? They can be all over the map.

Tom: if the filaments are being affected too much, you might consider taking the filament windings off the flyback and moving them to a step down transformer. Take a 120v primary transformer from something small like a clock radio, and remove the secondary windings. Replace those with a few turns of HV wire and run that to the rectifiers, the current you save won't have to come from the flyback anymore and may just give it the oomph it needs to make respectable pictures again. You could test the theory by temping in some 1.5v batteries to power the rectifiers, if it doesn't help at least you didn't spend any money. Just a thought.

Good to hear that some CT-100s can produce a bright stable picture. Do you think the CRT is the difference? Normally I might expect a high emission tube to have greater danger of loading down the HV than a lower emission tube. Or maybe a tube with more usage somehow "wastes" electrons on something other than lighting up the screen?

Since the set is reasonably functional as a black and white TV at the moment, I'm looking into why there is no color. It looks like this will be a fairly labor-intensive bring-up.

The first problem I noticed is that the chroma reference oscillator does not run properly. It fires up for a few milliseconds, and then goes quiet for about 1/2 second. This cycle repeats continuously. I found that this behavior is occurring because as soon as the reference oscillator produces a signal, it causes the chroma sync phase detector to output a strongly negative signal, which has the effect of shutting down the oscillator (I'm not sure a negative signal to the reactance tube should cause the oscillator to shut down, but it does). Adjusting the tuning of the phase detector transformer has no effect. If I short the output of the phase detector to ground, the reference oscillator runs continuously. I haven't found any bad components under the chassis in the surrounding circuitry (except the 100 meg resistor in the color killer circuit, which I replaced), so I will check the coils and transformers next. Everything is recapped, including most micas at this point.

[new info] - When I short the phase detector output to ground so the reference oscillator runs freely, it turns out that its frequency is 2.47 MHz, not 3.58 MHz. Furthermore, it keeps right on running at 2.47 MHz if you pull out the crystal, and when the crystal is replaced with another 3.58 MHz crystal. So perhaps the tuned circuits do indeed need some attention. Will check that this evening. Maybe the phase detector is fine, simply doing what it does when the reference oscillator frequency is way below target.

Another problem I notice is that if I look at the output of the first video amp on the scope, the chroma sync burst on the back porch of the horizontal sync pulse is not visible. I gather this is probably a video IF alignment issue, causing insufficient bandwidth to pass 3.58 MHz? I suspect that's a big problem, so will do an IF alignment soon. Adjusting the fine tuning doesn't seem to provide any setting where the chroma sync burst comes through, at least not without a general massive increase in noise as I tune beyond the point where the black and white video looks reasonable. I imagine if I can't see the chroma sync burst, there won't be any chroma signal getting through either, so color is not going to happen even if the reference oscillator is brought to life.

Got the chroma reference oscillator fixed. It's an oscillator design that is new to me, and is quite sensitive to the value of a "choke" in the control signal from the phase detector back to the oscillator to adjust its frequency. Although Sams calls it a "choke," that is quite a misnomer -- it's actually really an inductor with a specific value affecting some RF response on the control line. Put in a coil much more closely matched to the original and got it running OK.

Still no color, however, so I ran some checks on the video alignment, and found things are not even close. This explains the lack of chroma sync burst on the detected video and so-so sharpness on the black and white picture (apart from focus issues). It appears that virtually every slug on this set has been fiddled with in the past. It's got traps in the middle of the passband, the wrong center frequency (by more than 2 MHz!), a generally peaked (rather than flat) and narrow passband shape, and worst of all, one of the little IF coils in the tuner pushed inside the tuner and damaged (core cracked and stuck). I'm repairing that coil -- nice that that top of the tuner comes off so easily for service.

Alignment looks like it will be very time consuming... and may uncover some additional problems.

Convergence transformer arrived today, so that is also ready for attention. Lots to do.

Are you aware of the chronic problem these sets have with video peaking coil failures?

I restored a 21CT55 CTC2B chassis and that inductor in mine had also failed. Like Electronic M says, the peaking coils are common trouble areas. Check all of your inductors and suspect all that are coated in a white cement like substance. It seems to corrode everything it touches.

The CTC2 and CTC2B are similar in a lot of areas. When I aligned mine I found it helpful to inject a color bar pattern at the 1st video amp (pulling the last video IF tube) and get the video and color problems fixed before getting a final good RF/IF alignment.

Dave

I came across lots of good info online about the failure of coils in these sets. I tested all those first thing when I started and replaced five that were open. I thought this particular one in the chroma reference oscillator circuit wouldn't be particularly critical in value, since it appeared to be an RF choke intended to pass only low frequencies. That turned out to be an incorrect understanding of how that oscillator is designed, so I guess I created my own problem in the process of replacing that coil. Once it was replaced with one close to the original value, the chroma reference oscillator started working.

The circuit is basically a phase locked loop, and usually the control voltage output by the phase detector would be filtered to remove all trace of the RF. Such is not the case here -- apparently a significant RF component appears on the control line and needs to be there for the oscillator to function properly. An unusual design to me.

I'll keep an eye on the remaining white coated coils in this set, since they are obviously subject to failure sooner or later as well.

Dave, thanks for the tip on feeding a composite video signal into the video amp; that sounds like a good "divide and conquer" approach. Since I can't get a nice video signal through the IF chain just yet, that might be a morale booster to get some color on the screen earlier in the process!

After a full evening's work on IF alignment, the video IF response looks better. Not an exact match to what Sams thinks would be ideal (rolloff slope on high end of passband is too steep), but hopefully OK?

The first photo is the bench setup. Second is the connection to the tuner I used for injecting the IF sweep for quite a few of the alignment steps. This has very short leads (less than 1" beyond the shield). The third picture is the IF response from injection point at the diode in the tuner through to the video detector. Although I don't show my markers here (they are not very photogenic on the scope), I have the scope carefully calibrated, with the center being exactly 44 MHz, and each division exactly 1 MHz. The null point on the low end is 41.25 MHz, and the top end goes to zero just under 47 MHz.

Alignment of this set is quite an undertaking compared to a typical black and white set, which I can usually align in a pretty short time. And there's still plenty more to do in the color circuitry.

Wow! I've never seen a response that excellent. No wonder those
sets give great pictures. Is a 21CT55 as good?

Yes, they have the same IF and are both a royal bi!tch to align if you aren't careful.

Well, today there were several steps forward, and one big step backwards.

Was still having trouble getting the chroma reference oscillator to lock properly, and then figured out that I had a grid emission problem on the 6AN8 in the oscillator. A voltage check found the grid of the reactance tube much too positive given what the circuitry around it was doing. After swapping that tube out (it looks fine on a tester), I was able to lock the chroma oscillator. At that point, I had lots of wild colors on the screen, and got busy with alignment of the chroma bandpass filter and various other tuned circuits in the color demodulators. Then worked on purity, which was only so-so around the edges (maybe I need a degausser?). Finally installed the new convergence transformer. While setting up to do convergence adjustments, I adjusted the width, height, linearity, to get a nice looking crosshatch on the screen. So far so good, and then...

I heard a gentle pop, and the picture went dark. Very quickly took a look at the flyback, and low and behold, the tape holding the 3A3 anode lead in place had actually caught fire! Obviously an arc occurred (maybe triggered by my changing the width setting?). Quickly blew out the flame, and then pulled out the flyback to see what condition it was in.

Quite surprisingly, all windings good, and no shorts. Good ringdown. But it would obviously arc again without repairs. I unwound a few layers from the outside diameter, and am coating with corona dope and varnish while I contemplate what to do next.

There were significant problems running things with reduced HV because of the turns I previously removed from the flyback, so simply getting back to where I was earlier today probably isn't a real solution.

If I add more turns to this flyback, I wonder if it will arc again? Doesn't look promising.

Maybe tomorrow I'll try a voltage tripler running of the primary of the flyback. If I get enough voltage that way, I can remove the HV winding entirely. If I don't, maybe I'll unwind most of the HV winding, leaving just enough to run the tripler?

I wish there were someone out there with a spare flyback or a junker chassis or set. That would be a much more straightforward solution. But there might not be any spares out there that people are willing to part with.

Another solution, one I would use, would be to disable the HV system
entirely and find somewhere an appropriate Spellman HV-in-a-box supply and
use that until the correct working flyback turned up. And the HV regulation
would be spot on as these thing are really well regulated. I used to have several
... not on inventory! ... but they got thrown out by the disposal Nazis around here.
You can't hide a Spellman supply, just set in down on the floor of the cabinet.

This might cause a focus voltage headache however, and would of course
reduce the load on the whole horizontal system a lot and that would have to
be taken care of.

Maybe something like a HV board from an arcade XY monitor would be an idea for sets with unobtainium flybacks and parts.

They've been building replacement boards and flybacks for these on and off for a while, and they have the focus divider built in. 19KV is 19KV no?

Had to take a few days off from this project. Too many radios/TVs/hi-fis came in and the shop was filling up. Got those done, so back to this set.

With the current condition of my flyback, I decided to follow up on this great idea that was suggested way back on page 1:

Gave it a try this evening. Pulled the TCG523 tripler that has been serving very nicely in my Philco 48-2500 projection TV, and wired it up to the CT-100 chassis. I've got the HV winding of the flyback coated with a relatively thick coat of insulating red varnish, with the end of the HV winding buried in the varnish. That seems to be working OK to keep the HV winding from arcing right now. If this ends up being a usable solution, I'll coat it even better, or possibly remove it altogether.

The first picture shows the tripler on the bench temporarily wired up to the chassis. The input of the tripler is connected to the top of the primary -- the same place the 6BG6 plate is connected. The ground connection of the tripler is connected to the chassis, and the HV lead is resting against my HV probe.

Fired it up, and got 26-27 kV at the tripler output (see second picture). Putting the focus rectifier in place to provide at least a little load for the flyback lowers it to around 24 kV, which seems like a really lucky break. Just about right. The focus rectifier is wired as it originally was, off its own tap on the flyback, and powered by its own filament winding. The 3A3 HV rectifier is removed, and its filament winding not connected to anything.

Connected the tripler output to the HV regulator circuit in the set by touching the HV lead from the tripler to the metal housing of the 3A3 socket. The HV regulation works fine. If I set it to 20 kV, I get a mild red glow from the inside of the 6BD4 regulator (similar to what I had before at lower voltages when I was using the reduced-output flyback). Third picture shows the setup and the HV probe reading. I can adjust the HV from 16 kV to 22 kV with the CT-100's HV adjustment pot.

This looks like it may be a viable solution for dealing with my bad flyback. Will try it with the CRT next.

By the way, don't pay too much attention to the way I've got the replacement convergence transformer hanging off the back of the chassis. I will pot it in the original transformer housing once a few other issues are out of the way here.

Well, here's what I see on the CRT when using the tripler. Looks like there is plenty more work to be done on the color demodulator and video driver circuitry. Convergence is also pretty bad, so some serious work needed there as well. Anyway, this seems to be a step forward. My education in color TV continues...

Hi Tom, This looks like it's going to work!

So do we have any ideal of the circuitry involved in one of those HV tripplers? I'm assuming there are a couple switching transistors? Can't be too much going on in such a small package.

It's a classic half-wave voltage multiplier composed of a ladder of capacitors and diodes. A schematic can be found here: http://www.datasheetarchive.com/dlma...A879000-27.pdf . Look for the ECG523 diagram near the top of the page.

Now I remember seeing those schematics in my old ECG book. Amazing to think how something so common today, as a few silicon diodes, were keeping this circuit from being used back in the day.

6BG6 is a typo . . . isn't it? :worried:

Does 6CD6 sound better? 6BG6 was indeed a typo. Just finished a black and white set a couple of days ago and the two tubes look similar.