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#1
09-20-2011, 08:46 AM
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CTC-11 rebuild questions
Greetings all, I wanted to pose a few questions to my fellow CTC-11 collectors. In working on the 11’s restoration, I have encountered a few dilemmas…
• I cannot find a value for the thermistor on the primary of the power supply, except that it is 79 ohms cold. What are people doing to replace these? Mine was bypassed by twisting its leads together. I did find a 75ohm 4-amp part I purchased thru DigiKey. • The 3-amp circuit breaker was mechanically broken, where can these be obtained? • My 3A3 was replaced with a 3A3C which was shorted. I tested the flyback and it revealed 9 rings so I “assume” it survived. The plate cap to the 3A3 is burned and has green corrosion plus signs of internal arcing. Replace it or use a Dremel tool to grind the corrosion off and use the existing cap again? • Any reason I should not incorporate a ground buss for the circuit board ground pads on each board? My video IF board had every ground lug broken loose and a nice ‘cobble-job’ to create a ground using a spring! Perhaps a wire soldered to a chassis ground somewhere close that connects the grounds? Good idea or bad? Restoration update. So far; shorted 3A3C, open filament on the damper (6AU4 substituted with a 6AX4), shorted video IF (6GM6), nearly zero emission on the sound IF (6EW6), weak focus rectifier (1V2), a 6GH8 with zero emission (go figure), and a shorted X-Y demodulator (12AZ7). All of the OEM 6CG7’s were in run down condition with poor emission; all have now been replaced. In checking resistors, I was rather impressed most I could check were within tolerance. Two 22m 2-watt resistors (which DigiKey did not have) in the high voltage cage were off by about 40%, the three 100 ohm resistors on the convergence board were way high, a 150 ohm coupler in the video IF was about 30% high, and one bad 470 on the sound board. I suspect the set was run into the late 70’s, one FP electrolytic appears to have a date stamp of 1976 (I think). Are the board grounds a chronic problem with the RCA’s? It appears that most of the tubes that generated any kind of heat crystallized the solder on the socket lugs too. The Brookfield cabinet is buffed out, and the brown-black gunk on the CTR is cleaned off too, that crap is nasty! 
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#2
09-20-2011, 09:34 AM
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RE: The grounds. Try to maintain the original grounding scheme. Your plans sound OK to me. That thermistor is just a surge suppressor. 75 ohms cold is fine. Just so the hot resistance is near zero, so the chassis isn't starved. The 6AX4 isn't hefty enough to be a damper in a color set. Replace ASAP. All your proceedures seem to be in the right direction. When finished, it should be a great performer.
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#3
09-20-2011, 10:16 AM
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#4
09-20-2011, 02:02 PM
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Sounds like your 11 was an everyday driver. I'm surprised the mixer/oscillator in the tuner wasn't shorted too.
I haven't seen any of the circuit breakers in a while. Their reliability was very poor anyway. I have had to mount a fuseholder and use a slo blo fuse in place a few times. The thermistor could probably be ordered from McIntosh Labs, the audio manufacturer. The thermistor for their older (not reproduction) Mc275 works in place just fine and I think it is still available. It may not be the exact value but it warms up to nearly zero ohms. Check to see if the color oscillator has enough negative on the control grid. If it is low change the crystal with a big older style. The new (little ones) short out. And don't forget to check horizontal output tube cathode current. Nearly all the sets I work on show it too high which will cook the flyback. Let us see some pictures when it is up and running!
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#5
09-21-2011, 12:11 AM
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People may have different views on replacing the mylar "maroon drop" caps in these sets. My first CTC-11 (I have two) seemed to work well after replacing only electrolytics. It started to sag after a couple of years. Going back in and replacing the maroon drops (esp. on the sweep boards) made a world of difference.
When I later did my CTC-7, I showed the maroon drops no mercy. Life is too short to keep re-restoring a TV every time another marginal part fades out. Simpler to do a thorough job on the first go-round. I might feel more sentimental about originality if this were some precious early prototype, etc., but CTC-11 does not fall in that category. Just my $0.02. Phil Nelson Phil's Old Radios http://antiqueradio.org/index.html Last edited by Phil Nelson; 09-21-2011 at 11:06 PM.
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#7
09-22-2011, 07:39 AM
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Wanna be orange drops!
@Phil - after reading your narrative on your site, and others opinions within the rebuilder's community, I made the decision to go ahead and replace all of the burgundy drops! May be over kill to many, but I don't want to take the thing apart becasue another aged part had failed. I've already started the process of replacement which is nothing new to me. The worst I've done is a Sansui receiver with Dolby which had over 100 parts to replace. Philharmonics are not much different! Like you, I'd rather error in favor of not taking it apart with various stressed parts failing and do a little extra on the front side while it's apart. We also run at a higher line voltage today than we did 50 years ago, so... My conclusion, replace em! I will be replacing the diodes on the convergence board and main supply diodes which appear original too. I've heard of the silver mica's failing, but... I'll run it after lytics and maroon-drops are gone and see what happens.
@Bryan, I did find a circuit breaker at DigiKey that is 3A, and I'll mount a dummy breaker in it's original hole. On the top of the chassis next to the convergence socket is what appears a fuse hole that wasn't used along with a bunch of other vent holes. The replacement breaker will fit in one of these holes without any modifications so I think at this point I'll go that route. I will keep your offer in mind and contact you should I switch back to the original part. @26kc20, I plan to keep the group posted with both questions and progress! I'm excited to build something new to me vs. 70's Hi-Fi and 30's radios, add to that the assortment of 7" TV's I've done over the years... I did get the 75 ohm thermistor from Digikey that I'll try, but watch once power is applied... They don't give a running resistance, I suppose it's dependent on how much current the set draws and that part is a 4A part so it might not be a proper fit, it was only $2. By the way, I think your interested in the 60's rectangular sets too; on the restoration list is a 1970 19" table top remote 600 series Zenith metal box set. That might be next if the CTC-11 hooks me! Thanks for everyone's continued support! Bill
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#8
09-22-2011, 08:38 AM
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My CTC-9 has a fuse holder on top of the chassis in the hole you talk about. And yes, I get a kick out of some early rectangular colors. My Maggie t-933 is one of the favorites!
Always liked 11's. A friend's family had one in the 60's and they used that set forever. I couldn't tell you how many CRT's and flybacks went into that set. I think it was on at least 14 hours every day.
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#9
09-22-2011, 10:03 AM
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#10
09-30-2011, 11:46 PM
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Glad to see you guys are pointing WCF720 in the right direction. The only thing not addressed was the HV REC plate cap. Replace, replace, replace. Grinding the carbon off leaves sharp edges if even microscopic edges. Electrons have a funny way of tracking sharp edges. I can’t tell you how many Zenith sets I have hacked grinded and sanded trying to get the arcing to stop. Buckets of corona dope! It was funny to see how many customers elected the hack and butcher option as apposed to doing it right the first time. If there is ever a Computer Karma page I have a similar story for that one too.
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