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Old 02-11-2019, 10:50 AM
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My CTC-16XL Project.

The story so far: In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move...

Wait a sec, that's the Hitchhiker's guide to the galaxy...

The story of this RCA, found ( rescued ) from a High School vocational electronics class in the mid 80s, ( original problem , no color ), after some pretty dumb things were done to it, including , removing the color PCB.

I tried to fix it back then, but did not have much time to devote to it, since then, It has sat in storage waiting all these years, exposed to the cold of winter and the heat of summer. ( I'm sure the caps hated this, especially the electrolytics)

Last dec, I decided to pull it out and start working on it again, after much checking, I'm pretty sure ( not 100% ) that the color PCB is back in and hooked up correctly.
So, I dared to turn it on... no smoke, no explosions, no popped breakers, and after replacing the bad HV rec and reg, I got High voltage, and a raster ( very ugly ) no video yet. 21Fjp22a in great shape 3 good guns.

I'm still in the process of changing the main electrolytics, but I did see something a bit strange, C1a has been changed, but I still see a strong sawtooth wave there (before L45 and not after ) at about 10v when first turned on raising to 30v as tubes warm up and HV kicks on.

I'm pretty sure that sawtooth should not be there, or be that high, as mentioned, C1A has been replaced, (85uf 500v ) I may try something larger, I have NOT replaced C3B yet ( it may be coming from there.) and plan to replace the other electrolytics 1 at a time, to see if this goes away, I am also in suspect of the main LV rect diodes, they MAY be flaky, orig replacements are hard to find, so I'm guessing that 1N4005G dioded should be OK.

Once I get power stable on this thing, then I can worry about cleaning all the dirty pots and switches ( and tuner :/ ) and trying to get a video to show on it again...
I'm hoping that deoxit is a good choice for cleaning the tuner. :/

Last edited by Yamamaya42; 02-14-2019 at 12:26 AM.
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Old 02-12-2019, 03:25 PM
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As I mentioned, I am in the process of re-capping my RCA CTC-16XL,
The electrolytics mainly to start with, to get stable power, as it's been sitting for 30 years.
But there is one section in the multi cans, that does NOT look like power filtering, but part of AGC, and unlike the PWS section, if I replace with anything larger that what was in there, it can drastically change how it works.

C1 section c 40uf, ( see attached )
making a guess here, this is a feedback circuit off the output of video amp 2 , via the delay line, L13, L14, to set cathode bias on v6, (a/b) , so there is no wiggle room on that cap, it MUST be 40uf...
Am I reading it right?
https://imgur.com/a/iG2mCf6
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Old 02-12-2019, 03:54 PM
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C1 looks to be a cathode bypass/filter cap..... there's no such thing as a precision lytics in tube electronics....they all were rated -50% +100% capacitance tolerance. A 47uF or if your feeling persnickety a 39uF will both work fine.

40 is part of the old standard.of parts valuing that was on its way out when that set was new...So your not going to find a newly made 40.
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Old 02-12-2019, 04:06 PM
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Then the 56uF 80Volts cap I have should be OK then. but I'll replace that one last.

Last edited by Yamamaya42; 02-12-2019 at 04:27 PM.
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Old 02-12-2019, 08:50 PM
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update

I may be overthinking this, but to me , this sawtooth wave here (at C1a) just does not seem right, but the SAMS does not have a reference for a wave at that exact point, I have replaced C1a with an much larger cap and am still seeing it, its mostly filtered out by L45, but I don't think it should be there at all, its still present at the end of the 400v source ( very faint )

I'm running the set with HV disabled ( yolk disconnected ) when this wave was captured.
I have not replaced the LV rects yet ( they are hard to get to ) but I plan to, as I suspect them to be a problem. ( unless someone thinks that sawtooth I'm seeing is normal ) as mentioned, I chose 1N4005G for that as they looked rather close to what was in there..

https://imgur.com/a/U5mvTBT
https://imgur.com/a/6vEuABP
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Old 02-17-2019, 05:01 PM
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next update

replacing the LV diodes did not make that sawtooth wave at that point any better, so i't most likely normal, I DO get the 1v wave, as shown in the Sams on the other side of L45, i'm 1/2 way through replacing the main filter caps.
I still need to clean all the POTs and the tuner, to try to get it to get some picture on the screen, however, I may just bypass the tuner and IF all together and tap in video at the 1st video amp, to save time, ( around L9 ) as shown below.
https://imgur.com/a/PHTuOE9
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Old 02-17-2019, 05:12 PM
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The one thing i dread the most is... once all the electronic stuff is out of the way, fixing that damn cataract. T_T

https://imgur.com/a/d7cvF8P
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Old 02-17-2019, 06:22 PM
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That cat don't look too bad...A little more and it would fall off on it's own. Come summer put it face up in a 5 gal bucket or trash can, remove the tape around the edge, with a VERY thin screwdriver gouge out several 1" radius chunks of the glue (don't pry on the glass), then take halves of wooden clothes pins and wedge them in to the radiuses you removed, place it in the sun with a black garbage bag over it's face. Every 15-30 min tap the wedges in a bit. Gradually the safety glass will come off...The biggest enemy is impatience I've ruined 2/3 of the safety glass I've done this on by applying too much force too fast.

When your done peel and fingernail scratch all the old glue off, clean bulk residue with goofoff, then get streak free with glass cleaner. You can reattach the safety glass by at 4 even spaces along the edge placing 1/8"-1/4" thich foam double stick tape strips as gap spacers. then caulk the edge. Make sure it is ABSOLUTELY spotless before setting the glass on (any dust, spot or lint will be a pain to go back and get). And make sure the spacers and caulk are at least 1/4" outside the edge of the phosphor viewing surface...(otherwise, when the CRT is in the set you'll see it and be sad).
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Old 02-18-2019, 09:25 AM
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What kind of sucks now is, there is no easy way to test tubes... long ago, when I was a kid, there were testers all over the place, but now, if you go asking for one, they look at you like you have 3 heads and tentacles for arms. And yes, you can find some old portable ones on E-bay, but who knows how well they work, ( if at all. )
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Old 02-18-2019, 10:47 AM
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Quote:
Originally Posted by Yamamaya42 View Post
What kind of sucks now is, there is no easy way to test tubes... long ago, when I was a kid, there were testers all over the place, but now, if you go asking for one, they look at you like you have 3 heads and tentacles for arms. And yes, you can find some old portable ones on E-bay, but who knows how well they work, ( if at all. )
I've always considered drugstore testers as a waste of space.... get a portable like the B&K 606 I use predominantly.... any tester at this point is equally at risk of inaccurate readings. Most "portable" service testers have published service and calibration online. You can run thru a cal and if it fails just change a handful of resistors and caps and next time it should pass.

Also some tubes like sweep and HV cannot be accurately tested on any tester because no tester was made to deliver the high current and or high voltage the tube gets subjected to in normal applications. I seen plenty of HV rects and other sweep tubes where readings in multiple testers don't match actuall in set performance.

Nice anime catgirl avatar ya got.
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Old 02-19-2019, 04:50 PM
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Quote:
Originally Posted by Yamamaya42 View Post
I may be overthinking this, but to me , this sawtooth wave here (at C1a) just does not seem right, but the SAMS does not have a reference for a wave at that exact point, I have replaced C1a with an much larger cap and am still seeing it, its mostly filtered out by L45, but I don't think it should be there at all, its still present at the end of the 400v source ( very faint )

I'm running the set with HV disabled ( yolk disconnected ) when this wave was captured.
I have not replaced the LV rects yet ( they are hard to get to ) but I plan to, as I suspect them to be a problem. ( unless someone thinks that sawtooth I'm seeing is normal ) as mentioned, I chose 1N4005G for that as they looked rather close to what was in there..

https://imgur.com/a/U5mvTBT
https://imgur.com/a/6vEuABP
If you're getting a sawtooth waveform at first filter capacitor, don't be too surprised. These sets use a voltage doubler power supply, and it's going to have lots of ripple at the first filter. In other words, I'd kind of expect a sawtooth there.

Where did you get C1A from? What cap is it on the RCA schematic? Is that a sams or an RCA part number?

https://www.boxcarcabin.com/rcaschematics.html has most of the early rca schematics.

I sold my CTC16 some time ago, but it was a cool TV. Make sure to check for bad soldering of power resistors, and also I'd go over the chassis ground points. The spots where the boards are soldered to the chassis can cause intermittent issues if the solder isn't good, it would be a good idea to re-flow them. Clean all the tube sockets too.

Last edited by maxhifi; 02-19-2019 at 04:54 PM.
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Old 02-20-2019, 12:45 AM
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Quote:
Originally Posted by maxhifi View Post
If you're getting a sawtooth waveform at first filter capacitor, don't be too surprised. These sets use a voltage doubler power supply, and it's going to have lots of ripple at the first filter. In other words, I'd kind of expect a sawtooth there.

Where did you get C1A from? What cap is it on the RCA schematic? Is that a sams or an RCA part number?

https://www.boxcarcabin.com/rcaschematics.html has most of the early rca schematics.

I sold my CTC16 some time ago, but it was a cool TV. Make sure to check for bad soldering of power resistors, and also I'd go over the chassis ground points. The spots where the boards are soldered to the chassis can cause intermittent issues if the solder isn't good, it would be a good idea to re-flow them. Clean all the tube sockets too.
I'm going from the sams , that matches my CTC-16XL (set 812 folder 2 )
there is slight difference in the CTC-16 vs CTC-16X, so much that they have different releases . but both have full bridge rectifiers, and look nothing like voltage doubler in the link you shown (odd) , the bridge and C1 a is in a link i pasted above, Was 80uf, (400v) now is 100uf (500v)

I took a peek at all RCA color types leading up to the ctc-16, I'm not sure what rev that was in your link, but it's not a 16, for the following, when they came out with the 16, the voltage doubler was removed when they added the degaussing coil circuit, also, some of the tube types dont match up with what is in the set as shown.

Last edited by Yamamaya42; 02-20-2019 at 08:55 AM.
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Old 02-20-2019, 09:43 AM
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Quote:
Originally Posted by Yamamaya42 View Post
I'm going from the sams , that matches my CTC-16XL (set 812 folder 2 )
there is slight difference in the CTC-16 vs CTC-16X, so much that they have different releases . but both have full bridge rectifiers, and look nothing like voltage doubler in the link you shown (odd) , the bridge and C1 a is in a link i pasted above, Was 80uf, (400v) now is 100uf (500v)

I took a peek at all RCA color types leading up to the ctc-16, I'm not sure what rev that was in your link, but it's not a 16, for the following, when they came out with the 16, the voltage doubler was removed when they added the degaussing coil circuit, also, some of the tube types dont match up with what is in the set as shown.
There were about 6 schematics in the boxcarcabin link.... easy to miss unless you zoom out and scroll... The CTC16 a in 2 variants is there near the bottom.
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Old 02-20-2019, 10:42 AM
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On that RCA schematic it's C118a then, ( I did not see it at the bottom)
I still prefer the Sams, cause it's easier to see, and has much more info, like waveforms.
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Old 02-20-2019, 04:41 PM
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Quote:
Originally Posted by Yamamaya42 View Post
On that RCA schematic it's C118a then, ( I did not see it at the bottom)
I still prefer the Sams, cause it's easier to see, and has much more info, like waveforms.
If C118A, then I would expect a sawtooth and that ripple magnitude sounds about right. That sawtooth is just the capacitor discharging as load current is drawn and then recovering as the rectified AC input waveform recharges it. The ripple is high here since this is the first filter capacitor.

For checking tubes, substitution is always your best bet. It would make sense to have on hand spares for most of the tubes in that set. Drugstore testers were more about tube sales than thorough tube testing.. for a really good test, a mutual conductance type tester is always best, but not really worth getting until you're surrounded by tube equipment needing repair. If you want to find one locally, figure out where audiophile, ham radio enthusiasts, or antique radio collectors hang out, you'll probably be able to borrow one, or at least bring your tubes to someone to check.

Last edited by maxhifi; 02-20-2019 at 04:47 PM.
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