RCA CTC...Something? poor HV output.

[old_coot88]

Since that boost diode's been replaced with silicons, be sure to monitor it (them) for overheating.
The original part being selenium, it could handle the fast retrace ("fly-back") spike whereas silicons lagged in fast-switching ability.

It might be worth asking somebody like Mouser or Digikey if they've got Schottky diodes in high enuff voltage rating. Or you could series 'em.

[Electronic M]

Originally Posted by old_coot88

Since that boost diode's been replaced with silicons, be sure to monitor it (them) for overheating.
The original part being selenium, it could handle the fast retrace ("fly-back") spike whereas silicons lagged in fast-switching ability.

It might be worth asking somebody like Mouser or Digikey if they've got Schottky diodes in high enuff voltage rating. Or you could series 'em.

Honestly, my Silvertone CTC-15 clone had to have it's Boost rect changed 5 years ago....Back then I used the same diodes to replace it, and those have been in weekly to daily use ever since without issue.....If they fail in the first 2 years of service I will be shocked.

[Findm-Keepm]

We always used an RGP15-20 for any scan derived power supplies. It's a fast recovery 2000V 1.5A diode, and works perfectly in my CTC16, and cheap at a quarter for one diode, far cheaper than the NTE506.

http://www.fagorelectronica.com/imag...or/rgp1520.pdf

RCA specified this type in the later chassis(M134, CTC203) and once we figured out the root part number, we ordered a bunch and never looked back. great for boost diodes, and convergence diodes.

Conventional diodes like the 1N4007 and 1N5408 are just too slow, and tend to overheat.

[Electronic M]

Quick progress. The only vertical stage resistor under 2M I did not check (excluding controls which I skipped last session) was near the controls, and it was wide open....R102 150K .....I replaced it with another one on the top end of it's tolerance (t'was all I could find ATM).

Replacing it got me this.


I can't get linearity quite right though.....If I do the bottom (and sometimes top) is under-scanned, and centering is maxed downwards.....It's progress though.

This is the HO tube that died. I can't find any ID marks on it.

[Arcanine]

Originally Posted by Electronic M

Quick progress. The only vertical stage resistor under 2M I did not check (excluding controls which I skipped last session) was near the controls, and it was wide open....R102 150K .....I replaced it with another one on the top end of it's tolerance (t'was all I could find ATM).

Replacing it got me this.


I can't get linearity quite right though.....If I do the bottom (and sometimes top) is under-scanned, and centering is maxed downwards.....It's progress though.

This is the HO tube that died. I can't find any ID marks on it.

Oh... crap... That's one of my Dentron part numbered tubes. It's an unusual 6LQ6 tube. I tried it in the TV early on, and found it only works in HF amplifiers and not televisions despite being the same number. It's an optimized tube for HF amplification and not television.

Dentron's part number for those is D-50. http://www.radiowrench.com/sonic/so02182.html is what it came out of.

Those... are very expensive and hard to find (At least they were 9 years ago. Not looked in a long time). I forgot it was in that lot of tubes. I need to know if that RCA 6LQ6 tests healthy, if it does I can rearrange the HF amp's tubes and use the RCA as the driver.

If you don't mind test that RCA H-Out tube for me.

Don't worry dude accidents happen. I'm not mad at you. I'm MUCH happier to see a full picture on the screen of that TV then I am upset over a broken Dentron tube.

[Electronic M]

About done.

I went after the vertical linearity issue this past week. I made sure all resistors in the circuit were good and changed any marginally bad testing caps. One odd thing I found is that a cap in the output cathode circuit was listed as a .47, but the original installed part was a .15uF....I stuck with the value was installed after trying a .47 with no improvement.
I'm not proud of my replacement for that .0082 1KV orange drop....The best I could do, since I don't stock new caps over 630V, was to connect a few 2KV rated blue disc caps salvaged from 90's BPC sets in parallel for the correct value as measured on my cap testers.....Not pretty, but it should function well...It's the kind of thing I regularly put in my sets when there is nothing better on hand, but I prefer not to do that in sets repaired for others (looks unprofessional, and I'm not right there laying in wait to replace if it fails).


The vertical linearity issues were watchable, but bad enough to bother me.....After all that passive part verification (with little improvement) I was about ready to give up and say the linearity was not going to get better, but then I remembered that when it still had the under-scan issue tube swapping showed linearity differences....So I swapped the vertical tube and things got better...Much better.


One odd thing that happened is that after around 1 hour on the flyback got rather hot....I know because I started smelling wax, then heard a sizzling noise from the HV cage. As soon as that happened I switched it off and opened the HV cage immediately the sizzling continued and was visually confirmed to be coming from the center of the fly windings, and a drop or two of wax had freshly landed on the small existent wax stalagmites. Many of my sets have evidence of this happening before and during my ownership, but I've never seen or heard it in action before....So I don't know whether to interpret this as normal or a warning sign. I had checked cathode current to be just under 200mA not more than 5 minutes before this happened.....
5-10 minutes after powering it off I powered it back on to do a few adjustments for 10-20 minutes....It worked fine, and it did not sizzle again.
Might be a good idea for you to drill some vent holes in the HV cage and add a computer fan to help cool it.

At this point all there is worth doing is to test all the tubes, test the lytics/replace any bad ones (if present) and reassemble it. The cans were cool after over an hour run time, and it's working like a champ, so I'm not sure the tubes and lytics need my attention.....If you want me to I'll go over them, otherwise I could skip them for speed.

Chroma synch has been reliable, but I make no guarantees that it will hold after a bumpy car ride back to your place, so I'll give you some instructions on how to adjust it when you pick it up.

If you are worried about the fly I could work on the CTC-20 after returning the 16....Then if the 16 dies (and if I can fix the 20) I could swap you a working CTC-20....

Let me know what you think.

[Arcanine]

Originally Posted by Electronic M

About done.

I went after the vertical linearity issue this past week. I made sure all resistors in the circuit were good and changed any marginally bad testing caps. One odd thing I found is that a cap in the output cathode circuit was listed as a .47, but the original installed part was a .15uF....I stuck with the value was installed after trying a .47 with no improvement.
I'm not proud of my replacement for that .0082 1KV orange drop....The best I could do, since I don't stock new caps over 630V, was to connect a few 2KV rated blue disc caps salvaged from 90's BPC sets in parallel for the correct value as measured on my cap testers.....Not pretty, but it should function well...It's the kind of thing I regularly put in my sets when there is nothing better on hand, but I prefer not to do that in sets repaired for others (looks unprofessional, and I'm not right there laying in wait to replace if it fails).


The vertical linearity issues were watchable, but bad enough to bother me.....After all that passive part verification (with little improvement) I was about ready to give up and say the linearity was not going to get better, but then I remembered that when it still had the under-scan issue tube swapping showed linearity differences....So I swapped the vertical tube and things got better...Much better.


One odd thing that happened is that after around 1 hour on the flyback got rather hot....I know because I started smelling wax, then heard a sizzling noise from the HV cage. As soon as that happened I switched it off and opened the HV cage immediately the sizzling continued and was visually confirmed to be coming from the center of the fly windings, and a drop or two of wax had freshly landed on the small existent wax stalagmites. Many of my sets have evidence of this happening before and during my ownership, but I've never seen or heard it in action before....So I don't know whether to interpret this as normal or a warning sign. I had checked cathode current to be just under 200mA not more than 5 minutes before this happened.....
5-10 minutes after powering it off I powered it back on to do a few adjustments for 10-20 minutes....It worked fine, and it did not sizzle again.
Might be a good idea for you to drill some vent holes in the HV cage and add a computer fan to help cool it.

At this point all there is worth doing is to test all the tubes, test the lytics/replace any bad ones (if present) and reassemble it. The cans were cool after over an hour run time, and it's working like a champ, so I'm not sure the tubes and lytics need my attention.....If you want me to I'll go over them, otherwise I could skip them for speed.

Chroma synch has been reliable, but I make no guarantees that it will hold after a bumpy car ride back to your place, so I'll give you some instructions on how to adjust it when you pick it up.

If you are worried about the fly I could work on the CTC-20 after returning the 16....Then if the 16 dies (and if I can fix the 20) I could swap you a working CTC-20....

Let me know what you think.

I honestly never thought I would see that TV produce even a half watchable picture. That is as close to perfect as I'd call a set that old.

I would not worry about your repair. I can source a new cap and replace it if your repair ever fails.

As for the Flyback, I had the same thing happen where it got very hot for no reason what so ever. Judging by the wax build up in there, it's been doing that for a very long time for no real reason. Unless it's acting up internally, like windings have fused or something.

Maybe someone here has a spare CTC16 Fly I can get as a spare.

As for the rest of it, it looks like it has a great picture. Pretty excited to see it's alive and working again.

[Electronic M]

Glad your happy with it. Roundys tend to be a pain in the but to fix for first timers, but often teach them a lot about what can and will go wrong in these sets.

Do you want me to check the tubes and or lytic cans, or should I just bolt it back together and call it done?

[Arcanine]

Originally Posted by Electronic M

Glad your happy with it. Roundys tend to be a pain in the but to fix for first timers, but often teach them a lot about what can and will go wrong in these sets.

Do you want me to check the tubes and or lytic cans, or should I just bolt it back together and call it done?

Yeah go ahead and test them. May as well make sure they're okay before calling it gone be cause I plan to put it in to service and actually watch the thing.

Make sure you find a good 6LQ6, for me, too.

[DavGoodlin]

This brings back good memories from all the CTC12s-16s I worked on in my HS years, when I had lotsa time -
thanks for a great thread

[Electronic M]

Originally Posted by Arcanine

Yeah go ahead and test them. May as well make sure they're okay before calling it gone be cause I plan to put it in to service and actually watch the thing.

Make sure you find a good 6LQ6, for me, too.

Will do.

I have only one good spare 6JS6/6LQ6 in my stocks. I kinda hate to let go of it since that CTC-20 needs one (HO socket is empty), and I have at least 6 working sets that use that tube...

I wish I could trade some other sweep tubes that I have in duplicate++ for some 6LQ6 tubes.

[Arcanine]

Originally Posted by Electronic M

Will do.

I have only one good spare 6JS6/6LQ6 in my stocks. I kinda hate to let go of it since that CTC-20 needs one (HO socket is empty), and I have at least 6 working sets that use that tube...

I wish I could trade some other sweep tubes that I have in duplicate++ for some 6LQ6 tubes.

I sent you a DM about the tube situation, Tom. Keep your spare dude, you have a stack of sets that use it. That TV is the only I have that uses those. I have a half life one I can give you for the CTC20. It'll work in a TV fine, but my HF amp can't use it.

I believe there might be one more label less tube like the broken one in the bunch from me, along with an RCA 6LQ6, and then the 6LQ6 that was actually in the TV it self. I need to know you still have those two, I went looking and I am missing two. Pretty sure I tried two tubes.

[old_coot88]

Originally Posted by Electronic M

...
I have only one good spare 6JS6/6LQ6 in my stocks.

You meant 6JE6, right? (6JS6 is 12 pin.)

[Electronic M]

Not counting the broken tube or the tube presently installed in the CTC-16; I have 3 loose 6LQ6 tubes in the boxes you brought me. One unmarked (likely Dentron), one RCA and one Sylvania. The unmarked one tests 50 on my tester (upper end of the bad tube zone), the others test in the 90 range.


I tested almost all the tubes you brought me (three in the brown box and the ones in the CTC-20 were not gotten to yet). One 6GH8 in the boxes was bad. I replaced a bunch of tubes in the CTC-16 most tested healthy, but failed the grid emission and or short test of my tester....There were some weak ones, the HV rectifier, the audio output, and the 6GH8 that was NOT in the chroma osc. circuit.....Both 6GH8s were replaces since both failed in some way. Your set also now has one of two nuvistors I've had in my stocks for years....I was dumbfounded that I was able to locate one, and that it was the right type.


The tubes that are not weak (most of them) likely would be fine to use, but I replaced them with better ones (mostly from my stocks) anyway....You can use the old ones as spares since it was working fine with them in place. I also put two of my good 6GU7s into the spares bucket to make up for the original I ruined.
The new tubes did not significantly change the performance aside from (I think) better color lock, and reception strength.


BTW the spares boxes contained 2-4 tubes that fit the 20, but not the 16. Do you want those or should I pop them in the CTC-20?

Yes Old_coot, you are right, I either miss-typed or jumbled the number in my head.

I'm going the heck to sleep now. I'm exhausted.

[Arcanine]

Originally Posted by Electronic M

Not counting the broken tube or the tube presently installed in the CTC-16; I have 3 loose 6LQ6 tubes in the boxes you brought me. One unmarked (likely Dentron), one RCA and one Sylvania. The unmarked one tests 50 on my tester (upper end of the bad tube zone), the others test in the 90 range.


I tested almost all the tubes you brought me (three in the brown box and the ones in the CTC-20 were not gotten to yet). One 6GH8 in the boxes was bad. I replaced a bunch of tubes in the CTC-16 most tested healthy, but failed the grid emission and or short test of my tester....There were some weak ones, the HV rectifier, the audio output, and the 6GH8 that was NOT in the chroma osc. circuit.....Both 6GH8s were replaces since both failed in some way. Your set also now has one of two nuvistors I've had in my stocks for years....I was dumbfounded that I was able to locate one, and that it was the right type.


The tubes that are not weak (most of them) likely would be fine to use, but I replaced them with better ones (mostly from my stocks) anyway....You can use the old ones as spares since it was working fine with them in place. I also put two of my good 6GU7s into the spares bucket to make up for the original I ruined.
The new tubes did not significantly change the performance aside from (I think) better color lock, and reception strength.


BTW the spares boxes contained 2-4 tubes that fit the 20, but not the 16. Do you want those or should I pop them in the CTC-20?

Yes Old_coot, you are right, I either miss-typed or jumbled the number in my head.

I'm going the heck to sleep now. I'm exhausted.

The unmarked is a Dentron yeah. Internally something is different about them, that they got their own Dentron part number, and refuse to work inside of a television. So as a result they never test quite right. I know it's good because last time I transmitted with the amp on full blast, I was seeing some pretty sweet RF power.

The 6JE6/6LQ6 that's installed in the CTC16 now (Or rather when I delivered it to you) is actually from the CTC20 originally (It's hat looks more like that of a HV Rectifier). I swapped them around. Go ahead and take it out and keep it, and pop my spare RCA back in. That gives you an HO tube for the CTC20 then.

As for the tubes that DON'T belong to the CTC16, those belong to you now. I just popped a pile of tubes out of the CTC20 the final time I decided to mess with the CTC16.

Let's arrange pick up in the next week or two. Mom's car is in the shop currently getting the transmission replaced, so I don't have a warm safe SUV to transport it home in currently. And with it supposed to rain most of this week, the bed of my truck is not a good idea.

And do not buy what the tester says. Jim will chime in and agree, HV Rectifiers never test correctly. They almost always test as bad. Same thing for the Focus 1V2 tube, they test almost bad. You have to remember, the tube usually has 25kW pumping though it, so the tester can't even scratch the surface. Jim and I tested almost 10 of those tubes and they all tested pretty much the same. "Bad"