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-   -   Rca CTC-25 overview and help (http://www.videokarma.org/showthread.php?t=271064)

ZenithNut 11-12-2018 07:50 PM

Rca CTC-25 overview and help
 
Hello,

A while back my prayers for a tube color set got answered with an rca ctc 25 combo. Its a "halmstead" in walnut veneer modern danish styling. It has a 1972 date code "black matrix" 23valp22 crt in it that tests dam good on my bk 467. Emissions barely drop if you dial the heater voltage down to five volts.

Initial power up was great. However after sitting around my house moisture penetrated the flyback. The last time I powered it up It still had hv but man you could hear it fizzing and hissing in there. Ive since not powered it on again.

Id like to maybe re wax it or seal the flyback with corona dope or rtv silicone. Id also like to get a spare flyback for this set as id like to use fairly often. Used or nos. If used id probably recondition it in a similar fasion to prevent future failure from moisture.

Does anyone have any method of repairing these?

Moyer electronics last a tried was clean out. Same with the early television museum. Ive found one guy in the facebook group vintage television collectors who has one but he wants a $$$ for it which is fine and im completely willing to pony up. I just wanted to try here as well.

I do have the sams and a 1967/68 rca color television manual that covers my set.

I am amateurish as far as experience with tvs go. I have this color set and a bw zenith. Ive mostly done old tube radios and tube stereos. I do have most basic test equipment except a pattern generator and hv probe but thats ok.

Electronic M 11-12-2018 11:18 PM

If you have HV your fly is still decent. There are a variety of things in the HV cage that can cause that noise. First off the HV cage and the parts inside it need to be VERY clean...Even a thin hard to notice layer of dust can carbonize into a conductive path.
Second: the filament leads between the flyback and the bottom of the HV rect tube and the insulator cup around the base of that tube as well as the HV lead to the CRT and the top lead to the HV regulator can all break down and arc/ develop holes and or conductive carbon tracks fron HV side of the insulation to grounds on the outside of the insulation (I've seen and fixed these issues many times)...Examine it thouroughly with the set on and covers open with little to no room lighting to acertain the exact source of arcing, and if you clean these parts (which you should) examine them carefully.

Third (it has been a few years since I last had a CTC-25) IIRC these molded the top cap of the HV rect tube into the fly HV winding....If the HV rect tube is too physically short it will not seat properly into the cup and arc...Makesure you have one of the taller versions of that tube (different makes made them taller and shorter at different times). Also on RCAs with the HV top cap molded into the flyback there is an issue with the outer rubber tire breaking down and becoming conductive between the cup and the center of the winding. The solution is to peel off the rubber tire scrape away any carbonization beneath the tire and recoat the area the tire once covered with sensor safe RTV silicone.

Another note in the days these sets were new many people in humid climates did not own airconditioners or dehumidifiers, and these sets were designed to handle it. If the fly absorbed too much from being off for weeks/months it would heat up and boil/bake out the moisture sometimes bubbling out a bit of wax too, then normalize and continur to function...If you recoat it before letting it do this maybe leave a small breathe hole or two on the side for it to vent then seal them after it has baked out a good bit.

Also important is making sure your horizontal is set up properly the osc, needs to be adjusted properly as per the sam's proceedure, grid drive/bias at the horizontal output needs to be strong, and perhaps most importantly yout H linearity/efficiency coil needs to be adjusted for minimum H output cathode DC current. All the horizontal adjustment proceedures should be explained in your copy of the Sam's...Preform them.

RCA flys can last indefinitely if you make sure conditions around them are ideal...If they engineered a bit more margin in like Zenith did then you could afford to be more lax with horizontal maintenance.

ZenithNut 11-13-2018 11:10 AM

Quote:

Originally Posted by Electronic M (Post 3205696)
If you have HV your fly is still decent. There are a variety of things in the HV cage that can cause that noise. First off the HV cage and the parts inside it need to be VERY clean...Even a thin hard to notice layer of dust can carbonize into a conductive path.
Second: the filament leads between the flyback and the bottom of the HV rect tube and the insulator cup around the base of that tube as well as the HV lead to the CRT and the top lead to the HV regulator can all break down and arc/ develop holes and or conductive carbon tracks fron HV side of the insulation to grounds on the outside of the insulation (I've seen and fixed these issues many times)...Examine it thouroughly with the set on and covers open with little to no room lighting to acertain the exact source of arcing, and if you clean these parts (which you should) examine them carefully.

Third (it has been a few years since I last had a CTC-25) IIRC these molded the top cap of the HV rect tube into the fly HV winding....If the HV rect tube is too physically short it will not seat properly into the cup and arc...Makesure you have one of the taller versions of that tube (different makes made them taller and shorter at different times). Also on RCAs with the HV top cap molded into the flyback there is an issue with the outer rubber tire breaking down and becoming conductive between the cup and the center of the winding. The solution is to peel off the rubber tire scrape away any carbonization beneath the tire and recoat the area the tire once covered with sensor safe RTV silicone.

Another note in the days these sets were new many people in humid climates did not own airconditioners or dehumidifiers, and these sets were designed to handle it. If the fly absorbed too much from being off for weeks/months it would heat up and boil/bake out the moisture sometimes bubbling out a bit of wax too, then normalize and continur to function...If you recoat it before letting it do this maybe leave a small breathe hole or two on the side for it to vent then seal them after it has baked out a good bit.

Also important is making sure your horizontal is set up properly the osc, needs to be adjusted properly as per the sam's proceedure, grid drive/bias at the horizontal output needs to be strong, and perhaps most importantly yout H linearity/efficiency coil needs to be adjusted for minimum H output cathode DC current. All the horizontal adjustment proceedures should be explained in your copy of the Sam's...Preform them.

RCA flys can last indefinitely if you make sure conditions around them are ideal...If they engineered a bit more margin in like Zenith did then you could afford to be more lax with horizontal maintenance.

Thank you very much. Thats all ver helpful and i will clean it up real well. The flyback hasnt melted down or anything. Any special cleaning solutions? Mild soapy warm water?

old_coot88 11-13-2018 11:34 AM

Quote:

Originally Posted by ZenithNut (Post 3205697)
... Any special cleaning solutions? Mild soapy warm water?

OMG, NO, nein, nyet!! :jawdrop:No telling what kind of conductive residues might get inside.:eek:

Electronic M 11-13-2018 11:44 AM

Quote:

Originally Posted by ZenithNut (Post 3205697)
Thank you very much. Thats all ver helpful and i will clean it up real well. The flyback hasnt melted down or anything. Any special cleaning solutions? Mild soapy warm water?

For most cases isopropyl (rubbing) alcohol is my preferred cleaning agent. On the metal cage, the HV cables and the plastic HV rect bottom cup (with all wiring and socket removed from cup if the dirt is especially stubborn I will use glass cleaner or goofoff as the cleaner.

ZenithNut 11-13-2018 01:20 PM

Quote:

Originally Posted by Electronic M (Post 3205699)
For most cases isopropyl (rubbing) alcohol is my preferred cleaning agent. On the metal cage, the HV cables and the plastic HV rect bottom cup (with all wiring and socket removed from cup if the dirt is especially stubborn I will use glass cleaner or goofoff as the cleaner.

Thank you.

Next time I power the set up I want to watch the current draw. I know the watts on it is 350. So the current draw shouldnt be over 3.2 amps or so once the sets warmed up.

I have a fluke 27/fm. How do i hook it up to watch the current draw? Do I put the negative of the meter to chassis ground and then the positive lead on one leg of the line?

Electronic M 11-13-2018 01:40 PM

Quote:

Originally Posted by ZenithNut (Post 3205700)
Thank you.

Next time I power the set up I want to watch the current draw. I know the watts on it is 350. So the current draw shouldnt be over 3.2 amps or so once the sets warmed up.

I have a fluke 27/fm. How do i hook it up to watch the current draw? Do I put the negative of the meter to chassis ground and then the positive lead on one leg of the line?

Line current and horizontal output cathode current have too loose of a correlation to be used interchangeably.

The cathode current can be measured by unsoldering the ground lead from the cathode pin of the h output tube socket then connecting the meter positive current terminal to that pin and the meter negative to ground (sometimes you should put a .47uF cap parallel to the meter ). The current will be in the neighborhood of 170mA to 230mA DC. make sure your meter has a 500Ma DC scale... I'm not familiar with your meter so check it's specs/manual. Also it is preferable to use an analog darsonval movement meter to a digital meter... it is a high frequency pulsed DC current on the cathode. An analog meter will average it well and be the same instrument that Sam's and the factory used to measure that. Some DMMs may get confused by non constant DC... I have not had that issue, but since I have an analog meter I use it instead of my DMM.... it is better for adjusting the efficiency coil for minimum current than most DMMs since it will show you minute changes that a digital display will hide in rounding to it's smallest digit.

One recommendation when you're done measuring the cathode current connect a new wire to the cathode pin, run it above chassis to a good spot to ad a fuse holder, ground the cathode thru a 1/4 amp fuse. Doing this will help protect the flyback from excessive current, and the fuse holder above chassis will also make a convenient current test point for future measurements... all you will have to do is remove the fuse and connect a meter across the holder terminals.

ZenithNut 11-13-2018 05:33 PM

Quote:

Originally Posted by old_coot88 (Post 3205698)
OMG, NO, nein, nyet!! :jawdrop:No telling what kind of conductive residues might get inside.:eek:

Got it!

ZenithNut 11-13-2018 05:58 PM

Quote:

Originally Posted by Electronic M (Post 3205701)
Line current and horizontal output cathode current have too loose of a correlation to be used interchangeably.

The cathode current can be measured by unsoldering the ground lead from the cathode pin of the h output tube socket then connecting the meter positive current terminal to that pin and the meter negative to ground (sometimes you should put a .47uF cap parallel to the meter ). The current will be in the neighborhood of 170mA to 230mA DC. make sure your meter has a 500Ma DC scale... I'm not familiar with your meter so check it's specs/manual. Also it is preferable to use an analog darsonval movement meter to a digital meter... it is a high frequency pulsed DC current on the cathode. An analog meter will average it well and be the same instrument that Sam's and the factory used to measure that. Some DMMs may get confused by non constant DC... I have not had that issue, but since I have an analog meter I use it instead of my DMM.... it is better for adjusting the efficiency coil for minimum current than most DMMs since it will show you minute changes that a digital display will hide in rounding to it's smallest digit.

One recommendation when you're done measuring the cathode current connect a new wire to the cathode pin, run it above chassis to a good spot to ad a fuse holder, ground the cathode thru a 1/4 amp fuse. Doing this will help protect the flyback from excessive current, and the fuse holder above chassis will also make a convenient current test point for future measurements... all you will have to do is remove the fuse and connect a meter across the holder terminals.

I will buy a 0-500 dc milliamp meter so that I may do that.

For the record though how can i set my meter up to look at the

Electronic M 11-13-2018 06:05 PM

Quote:

Originally Posted by ZenithNut (Post 3205724)
I will buy a 0-500 dc milliamp meter so that I may do that.

For the record though how can i set my meter up to look at the

Look at the what?

ZenithNut 11-13-2018 06:16 PM

Quote:

Originally Posted by Electronic M (Post 3205727)
Look at the what?

Do"h

I want to look at the overall ac current draw the set is using. I checked my fluke meter and it tops out at 320ma so an analog dc milliamp meter is on its way.

Electronic M 11-13-2018 07:45 PM

Quote:

Originally Posted by ZenithNut (Post 3205728)
Do"h

I want to look at the overall ac current draw the set is using. I checked my fluke meter and it tops out at 320ma so an analog dc milliamp meter is on its way.

On tube sets that test is much less informational than solid state. A meter that can't measure 5-10A AC can't directly measure the line current the set draws. (also some DMMs that can do 10A only do DC and some only do AC so knowing which the meter can do is important)....

All that said there is a way to indirectly measure the AC that set uses with your present meter (assuming it has an AC volts range) get a 5W or higher, 1 OHM power resistor place that resistor in series with one leg of the cord (can hack up an extension cord to do this (and make a universal adapter) ) then with the meter in AC volts range measure the voltage across that resistor...You can then compute the approximate current using ohms law: I=E/R= measured voltage/resistance...Given resistance should be 1 OHM that means measured voltage should be approximately equal to the current flowing. The accuracy of the resistor, the accuracy of the meter, where you connect the meter along the wire will all introduce some error to the measurement, but it should give a decent approximation.

ZenithNut 11-13-2018 08:11 PM

Quote:

Originally Posted by Electronic M (Post 3205736)
On tube sets that test is much less informational than solid state. A meter that can't measure 5-10A AC can't directly measure the line current the set draws. (also some DMMs that can do 10A only do DC and some only do AC so knowing which the meter can do is important)....

All that said there is a way to indirectly measure the AC that set uses with your present meter (assuming it has an AC volts range) get a 5W or higher, 1 OHM power resistor place that resistor in series with one leg of the cord (can hack up an extension cord to do this (and make a universal adapter) ) then with the meter in AC volts range measure the voltage across that resistor...You can then compute the approximate current using ohms law: I=E/R= measured voltage/resistance...Given resistance should be 1 OHM that means measured voltage should be approximately equal to the current flowing. The accuracy of the resistor, the accuracy of the meter, where you connect the meter along the wire will all introduce some error to the measurement, but it should give a decent approximation.

My fluke meter can go up to 10 amps ac/dc
Youve been really helpful so far. Cleaning out the hv cage and all the leads. I swore this hissing noise came from the back side if the cage. It will be a while till I get that dc milliamp meter in the mail.

One thing i forgot to mention is that one of the power resistors has been replaced on the chroma board. Also Ive been told theres a trace along that board that tends to fail. Fortunately mines in good shape. All ive done to it to add on is replace a few e caps and reflow the ground stags. Some have mentioned hard wiring the ground with a wire.

To touch up on your earlier post the ctc 25 does use a cup ontop of the flyback where the plate cap of the hv rectifier sits inside. I will wrangle up a few and see if it helps next time i power it up with a ammeter telling me what the cathode current.

If any of the wire insulation is at fault from breaking down (and this IS a high hour set) what would be a good replacement? I imagine regular old heat shrink tubing wouldnt be good enough for the 24kv..

Electronic M 11-13-2018 09:38 PM

If it is the filament lead/winding that has arced through check the wire's resistance before replacing it. If it is resistance wire it will be more of a task replacing it correctly.

If it is the HV lead that has failed or a non-resistive HV rect filament winding there are a few ways to go...All of them involve getting/installing new HV wire. There are probably vendors online that stock wire with 40KV rated insulation. Non-resistive spark plug wire from an auto parts store may work. I tend to just steal and reuse the HV leads from 1980's and newer CRT sets that folks abandon at the curb. The last option is the only one that comes with a HV connector on the end of the wire. The first two options require you to remove and reuse the existing CRT HV connector from the old wire if replacing the original HV lead to the CRT.

ZenithNut 11-14-2018 02:54 PM

Quote:

Originally Posted by Electronic M (Post 3205743)
If it is the filament lead/winding that has arced through check the wire's resistance before replacing it. If it is resistance wire it will be more of a task replacing it correctly.

If it is the HV lead that has failed or a non-resistive HV rect filament winding there are a few ways to go...All of them involve getting/installing new HV wire. There are probably vendors online that stock wire with 40KV rated insulation. Non-resistive spark plug wire from an auto parts store may work. I tend to just steal and reuse the HV leads from 1980's and newer CRT sets that folks abandon at the curb. The last option is the only one that comes with a HV connector on the end of the wire. The first two options require you to remove and reuse the existing CRT HV connector from the old wire if replacing the original HV lead to the CRT.


Got it! It wouldnt hurt getting a bpc tv to harvest other parts such as capacitors or resistors.


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