#1
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My "New" CT-100 restoration
I got my CT-100 from the ETF home safely. Thanks to Steve
for getting it all safely in the van. It appears mostly unmolested. I have tested all the tubes. A few were missing. One had a bad filament. Four tested weak, including the focus rectifier and the shunt HV regulator, but I have my doubts as to how well the Hickok transconductance checker did on them. The bottom of the chassis in very nice clean shape. The top has been partially cleaned and the rest is not bad. The HV cage is incredibly dirty. It took a huge quantity of alcohol to clean the tubes in it. What do people do to the parts inside? They clearly MUST be cleaned, but should I take it all apart or try to clean them in place. What cleaning agent do people use? Alcohol works, and won't hurt the ceramic caps, but what about resistors, especially the spiral high-ohmage ones? About half the white peaking coils are clearly bad, half appear to least to have the right resistance. More, including pictures, later. |
#2
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Some questions.
After careful examination, restuffing the chassis mounted electrolytic cans will be a nightmare if done as described in the article mentioned in the sticky thread at the top of this forum (remove can from chassis, uncrimp buttom) because they are all soldered in, most at two or three places. Some are riveted in. I'm not intending to leave the chassis bottom original looking, but I am the top, more or less. I could do a "cut off at the base and cover the gap with silver color tape" bit on them, but that would not look original even at a glance. What I'm thinking of doing is just leaving them in as is, removing them electrically, and adding terminal strips to hold the small new caps. For the ones in the power supply, I would remove the seleniums, which are huge, and mount the new caps, 1N4007s, and their associated dropping resistors, on a circuit board mounted inside their cage. The rest should easily fit under the chassis. What do people think of this ... it would be easily cosmetically reversible if a future owner wanted to, as I'm saving all the old parts. Where is the Candohm resistor on the schematic? |
#3
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I say this with all due respect and no malice whatsoever ;
Some sets , sure , I'd go the terminal strip route in a heartbeat rather than dive into the mess of wires required to do a "pretty" restuff . But a CT-100 , THE holy grail of tube color TV to most collectors , deserves , no , , really outright demands ! , that a proper cosmetic restoration accompanies the electronic restoration . In my view , historical value dictates the extremes one should go to in preserving the original looks , and what color TV would be more deserving of proper cosmetic restoration than your history making CT-100 ? Your set will only be virgin once ........ |
#4
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normally I don't worry about making it look completely original, I do cut off the cans and mount the alum tape back on , but that is for the sake of keeping lead dress the same. I never use term strips, just cut drill insert and solder. Sometimes I do not even bother with putting the cans back over the caps. Its just a TV and my only goal is to get it functional.
IF I had a CT-100 (which I prob would avoid since I would constantly worry about the CRT) I am sure I would go the extra mile to restuff by uncrimping and would also prob restuff the wax caps as well. It goes against my nature but due to the historical value of the set I think it deserves it. I think for me I would just look at it like this, its a one time deal, so take what ever amount of time is needed to do it right. Once its done its unlikely that that I would ever do again. |
#5
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Here are some pictures.
Edit: I should add that the original of the chassis bottom is about 10,000 x 10,000 pixels, as mentioned below. Last edited by dtvmcdonald; 07-18-2014 at 07:36 AM. |
Audiokarma |
#6
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And here are more.
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#7
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My goals may be different from some. Here they are,
in order of higher to lower importance: 1) Make the set work as originally intended, receiving signals at RF with full exact NTSC specs: including correct Q signal with 0.5 MHz double sideband and I with 0.5 and lower with 1.5 MHz bandwidth, even if I have to create these myself from RGB output of a DVD player. 2) Leave the top view of the chassis unchanged as far as possible. If there are bad controls I will try to find proper looking ones. There is a white peaking coil there, which I will replace, and a paper cap. The cap will be restuffed and I will make a little paper cap to cover the new coil, not perfect but will do. 3)Save all removed or replaced parts. I have made a 100 megapixel image of the chassis bottom so that a future owner could do a full restuff with proper placement. I'm not going to restuff anything under the chassis. 4) Leave the horribly dirty areas as clean as reasonable. This is not a 60's Tektronix scope, where the factory manual says to start a calibration with a good hosing down and sun dry! Water or even gallons of alcohol would damage coils. The cleaning has to be done with paper towels and Q-tips. Wires on the chassis top and insides the cages are filthy and slimy. Goop followed by alcohol seems to be the cure. That said, I have decided to not restuff the can electrolytics .. doing it without damage while unsoldering them from the chassis would be a nightmare and possibly beyond my skill. I'm going to compromise on point 1 above and remove the seleniums and install silicon diodes, their series resistors, and the new electrolytic caps for the power supply in the cage mounted on a fiberglass perf board. The board and caps will be painted bright orange. That will have to do for "the look" inside the cage. Doug McDonald Last edited by dtvmcdonald; 07-17-2014 at 09:25 PM. |
#8
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Hey those orange things with the fins are pretty neat looking.....
You gunna keep them the original color.....?
__________________
Yes you can call me "Squirrel boy" |
#9
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Quote:
some day sells along with the TV. They will be replaced with modern parts, completely different looking, painted that color. If you are unfamiliar with these sets, they are inside the perforated metal cage at left in the chassis top photo, and are essentially invisible if you look inside the set with the back removed. The top lifts off this set and they are visible, inside the cage, with the top off. Oh! I have another idea: series dropping power resistors have to be added in series with silicon rectifiers. I could use resistors intended to be mounted on heat sinks, and paint the heat sinks that color. The originals are 3 inches square. These could be as wide but only 3/4 inch or so high, leaving room for the caps I will put there. I'm feeling much better now about the original look! Ideas like that last one are why I am seriously over-planning this project. |
#10
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I have completed cleaning and recapping the HV cage.
This was a nightmare because it was so dirty and cramped. The 2.7 Meg 1/4 watt resistor was at 3.3Meg, and was replaced with an identical but in-spec part. The two 25 meg HV ones were right on the button. "After" photos are attached. |
Audiokarma |
#11
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Looks like a good start. There's no such thing as too clean, when it comes to the HV cage.
Take your time and enjoy. My theory with a project like this is that I may never get another chance to do another one of these. It's not a race, I sometimes have to remind myself. It's better to do a job right the first time than to beat some imaginary clock. And while the rest of us may offer advice or cheer from the sidelines, you are the ultimate arbiter of what is "the right way." Regards, Phil Nelson Phil's Old Radios http://antiqueradio.org/index.html |
#12
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Quote:
More and I get eyestrain and overexcited. This morning I went though the Sam's resistance to ground chart. The vast majority of the numbers are well within tolerance, most well within 10%, including most > 1Meg resistors. This is good news. This evening I will do the resistance to B+ part. I noticed that Sam's has a 12AT7 on their topside tube chart in a 7 pin socket! (Its really a 6AU6). I still have not got a reply to where the Candohm is in the circuit, and the nature of the 100 ohm resistors inside the chassis connected directly across its parts. Are these R286 and R287 in Sam's? The ".100" resistor in Sam's surely must be 100 ohms, otherwise there would be nowhere near -30v on the bias supply, as there can't possibly be 1.7A B+ current. |
#13
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Looking Good!
Quote:
The two U-shaped loops that you pictured earlier are "fuses" M-6 and M-7 in the heater supply... they are just short lengths of #26 wire enclosed in sheathing. jr |
#14
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OOPS! double post!
jr |
#15
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"All" I did today was disconnect the vertical convergence transformer from the
focus pot and its 0.01 uF cap and apply an external 5.2 kV through a 750 Meg resistor and a microammerter in series, for an hour (at room temp of course) to test the transformer "safely". (Safely for the transformer with the 750 Megs and safely for me with everything except the 5kV supply sitting on my 1/2 inch glass dining table.) It passed. Of course this is not forever at higher temps, but its better than fail. Doug McDonald |
Audiokarma |
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