A little Surprising, CT100 Fans

[John Folsom]

Nick, 1. Try adjusting the coil in the cathode circuit of the oscillator tube (make not o the starting position so you can put it back if the adjustment does not help). 2. Try adjusting the transformer in the plate circuit of the reactance tube. If this helps, then go through the color AFC procedure.

[miniman82]

Tried the coil in the cathode of the osc tube, no joy. Haven't yet tried the one in the reactance tube plate circuit, because I'm not sure what it does. This circuit is a lot different than the ones I'm used to playing with in later sets, most have the triode for reactance and the pentode for osc duty. But I'll mess with the other coil tonight when I get off work. What do you make of the scope trace coming and going?

[Phil Nelson]

If you master the color AFC procedure, you can come and do my set. I'm waiting to try it again until I get some more grown-up test equipment and develop a bigger brain

Phil Nelson

[miniman82]

AFC alignment isn't too bad, you just need a pair of meters and a good head on your shoulders. I think the problem with your set is the local oscilator is drifting too far off frequency, so far that it's beyond the phase detector's ability to pull it back in. Not sure why that is, but my guess will be the capacitors in the tank circuit drifting. When that happens, you won't be able to use the coil to get it back in spec. Same thing happened to my CTC-7, the osc coil is at the end of it's travel but it locks in.

[miniman82]

Just remembered I have a CTC-2B chassis, so I'm going to borrow both the reactance and oscillator cathode transformers from it to try and diagnose this issue.

[miniman82]

Swapped in the pair of transformers from the CTC-2B.....

....................


Nothing! Same result as before, so now I'm scratching my head because there's only 1 other cap and 1 other resistor in the whole oscillator. So while I'm sitting there wondering what my next move is going to be, I got a sneaking suspicion that something was staring me right in the face. I proceeded to put my DMM across the little inductor feeding the reactance tube grid and... INFINITE! Unbelievable! I swear this is the last time I ever trust these stupid little piles of crap, no matter how good they look. From now on, they will be replaced on sight no questions asked. I will install the rest of them from the kit I assembled later, since all I wanted to do up to this point is prove the chassis and tube worked well. Cabinet can now go off to the refinishing guy in Milwaukee.



After replacing the bastard little inductor, the scope showed that the oscillator now worked as it should. No more mysteriously shrinking waveform, and actually the open inductor explains why the proceedure for zero-beating the oscillator didn't work, since they have you ground the grid of the reactance tube through that same coil. Obviously, the result was dramatic: instant color lock!




Has a pretty obvious drive line now, I hadn't seen that before. Just another thing to add to the mental list of things to remember for later on. Right now I have a good chassis with color, and a tube with great emission just waiting for a nice cabinet to live in. I can't wait to drop it off, I just know Dennis will make it look like a million bucks!

[sampson159]

i have been following this thread intensely.so glad you have got it solved.post many pictures of the screen with images.you have worked hard and i am happy for your success.another ct 100 lives!

[Phil Nelson]

Originally Posted by miniman82

the little inductor feeding the reactance tube grid and... INFINITE!

The previous owner of my CT-100 had done some work on it, and he included a couple of parts bins in the deal. One of them had drawers full of little inductors. Seemed odd at the time, but I guess the inductors in that model are notoriously junky.

Those color bars look promising.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Pete Deksnis]

the brown inductors in a CTC2 chassis are not the problem. It is always the chalk-white ones that rot open after 40-years in a garage or attic, and even after 50- to 55-years under better environmental conditions.

Pete

[miniman82]

Yep, the brown ones always seem to be good, I think the white ones had something in the material surrounding the coil which causes the thin copper wires to corrode and open up. If you look closely, you can most times make out some green stuff on either end of the coil where the wire leads go into the body of the coil. That's copper corrosion. I tried repairing one once, but it's impossible. Even if you could get the lead in wire repaired, the coil is just as bad on the inside. I cracked one open with pliers, it's not a pretty sight. Anything the white stuff touches gets destroyed.

[ChrisW6ATV]

On the other TV forum, I asked if that was one of the infamous peaking coils... I can see from your picture (and description of green corrosion), the answer is "yes".

I am glad you have a raster on that set-nice progress.

[miniman82]

Here's the list of inductors which can be bought at Digikey for the CTC-2, a few have asked for it.

From phase detector to reactance tube grid: M10101-ND (1 piece)
Matrix output to CRT: M10093-ND (3 pieces)
Y-line, near delay line: M10082-ND (1 piece)
R-Y demod/amp: M10083-ND (2 pieces)
Q demod: M10098-ND (1 piece) and M10127-ND (1 piece)
Y-line near 2nd video tube, and matrix power input: M10106-ND (5 pieces)

[ChrisW6ATV]

Thank you for posting that list; I know some of my coils need to be replaced, and my CT-100 should be my next project before too long, I hope.

[miniman82]

Cabinet is off at the refinishers! Dennis asked me when I wanted it back: "this month or right before Christmas OK with you?" Man, this would be a sweet Christmas present to myself, huh?

[Electronic M]

A CT-100 for christmas......Can we trade places?

Just kidding.

Does sound like a nice Christmas present though.....