Today I have been working on an RCA CTC-28 I got from an estate sale a few months ago. I replaced the electrolytic capacitors and rectifier diodes and bypassed the degaussing thermistor as it had fallen apart. Also I relocated a wirewound resistor to the front of the chassis which had burned up wiring due to heat and replaced the burned wiring, and put a fuse in the power line input.

When I powered it up for the first time I got a raster but no picture or sound. I substituted the RCA tuner with that from a Zenith set hooked up to an isolation transformer and still didn't get anything but when the RCA tuner was hooked up to the Zenith set I got a good picture.

I then used the Zenith tuner IF output as a test signal source through a 100 pf capacitor and applied it through the IF stages of the RCA and found that it wouldn't pass through the last IF stage but there was weak sound when the signal was connected to the output of the last IF. It turns out the last IF tube was bad and when I replaced it I got good signal.

Then I did some modifications to the chassis consisting of using the power switch to control a 110 VAC coil relay to remove the high current load from the set off of the power switch. I added a terminal strip connected to the regulator 1000 ohm resistor and the horiz output cathode so I could test those easily with the chassis in the set and put in a fuseholder in the horiz output cathode for a 300 ma fuse.

I now have a pretty good picture with color but could use a little more contrast and to set up the purity. I measured the horiz output cathode current and it is 210 ma.

Here are some videos of the repair process:

Part 1: http://www.youtube.com/watch?v=L-bJ8IGz9Fg

Part 2: http://www.youtube.com/watch?v=z6ll5ByKAiU

Those are awesome sets and produce a great picture. I have been fighting at ctc35 with vertical issues. Turns out all those 'orange drops' go lossy and loose their defined value. After further investigation I found all the old red/orange drop caps in rcas are going lossy on all the sets I have.
Now that I got it working Im going to use it to make an IF/Chroma bandpass alignment video.
I wouldn't stress the 300ma cathode current fuse. Even if you pull the horizontal oscillator out the tube will red plate and never burn the fuse. You really need a chemical fuse for that purpose.
I have found the signal tubes like the IF one you found sometimes short if the set has been setting for a long period of time. A few good bangs on the table usually de-short the tube and it works fine.

Great videos and good to see someone else getting intimate with a late 60s CTC.

Thanks for your observations and advice. I know there were a few RCA tube-type portables (maybe CTC-22 and 36) that used a circuit breaker system in the cathode of the horizontal output tube. The breaker had a thermal element connected in the H.O. cathode but it ended up opening the contacts to the power line, cutting off all power in case of a tube overload. Maybe it was somehow more sensitive to dangerous overcurrent than a fuse would be?

The later tube type portables mounted a thermal fuse near the horizontal output tube and I think it was in the cathode of the tube...it must have been able to detect overheating in the tube in case of no drive or flyback failure.
For some reason I don't think there were ever factory overcurrent devices in the horizontal output circuits of the console sets.

I had a flyback fire when I was a kid, in a CTC-31...luckily nothing else was damaged but I left the room with the set on and came back and it was filled with smoke and the set was playing with sound...I really wanted to get an overcurrent device on the flyback system which would try and help prevent this.

Also I remember reading in an old magazine about Sprague Orange Drops having a dual dielectric...paper and Mylar. I'm thinking in the present day they are just Mylar. I wonder if these old 60's era orange drops are more prone to the type of degradation in paper caps but maybe not quite so dramatically as the wax/paper type or the black beauties?

Those are awesome sets and produce a great picture. I have been fighting at ctc35 with vertical issues. Turns out all those 'orange drops' go lossy and loose their defined value. After further investigation I found all the old red/orange drop caps in rcas are going lossy on all the sets I have.


CTC.

After reading this I wonder if I should worry about the maroon drops found in Zeniths also as I'm getting ready to do the recap on my Zenith roundie.

All the 'brown drops' in my '59 CTC-9 are perfect, but it is a very low hour set with a perfect CRT. I didn't bother replacing any of them, it only needed 'lytics and it works perfect to this day. Didn't even need convergence.

The wire type fuses act like a big resistor. Check the voltage drop and how hot the 300ma fuse gets in the cathode circuit. The chemical fuses have less resistance and a much tighter open threshold.

Those flybacks always seem to fail due to arcing in the secondary near where the rectifier sticks in the top of the fly. Probably due to all the heat.

Set the cathode current for minimum at full brightness.
Set the HV for 25kv at minimum brightness.
Check the drop accross the 1k cathode resistor on the shunt tube, if it exceeds 1 volt increase the hv untill you get to 1volt, check the HV again if it exceeds 27kv increase the HOT screen resistors value.
If the shunt tube resistor drop is less than one volt turn the efficiency coil clockwise until you get 1 volt drop staying under 220ma HOT cathode current.


If you are worried about X-rays set your target for 24kv at minimum brightness. You wont really notice it except on a weak crt although most likely you will have to increase the screen resistor to get the shunt tubes loading within spec.

Lowering HOT screen voltage reduces drive/hv/hot cathode current, turning efficiency coil clockwise increases it.

It a bit of a balancing act.

On the capacitors.

Hour usage has little if nothing to do with it. Davewm has a NOS Packard Bell he has the same issue with. I also have several NOS PBs with the lossy caps.

The only way to test this fault in the caps is an old school eye type tester. The eye wont open all the way with a lossy orange/red/brown drop.

It also appears to have allot to do with the circuit they are in. They drive the Vertical circuit nuts.

The symptoms are: poor deflection/linearity, one of the size controls at max, drift/size change with temperature/warmup, poor stability, having to adjust hold controls during warmup

It could just be the supplier rca and pb used in the late 60s. I dont remember running into this with Zenith or other sets.

Some of the caps
http://justsmog.com/Clay/BAD-CAPS.jpg

What is chemical fuse looks like (pictures or info)? I googled with no luck.

Cheers, Wizard

What is chemical fuse looks like (pictures or info)? I googled with no luck.

Cheers, Wizard

Its the one that is used in most Zeniths. Its a little rectangular box with two prongs. Also called a bell fuse.

On the capacitors.

Hour usage has little if nothing to do with it. Davewm has a NOS Packard Bell he has the same issue with. I also have several NOS PBs with the lossy caps.

The only way to test this fault in the caps is an old school eye type tester. The eye wont open all the way with a lossy orange/red/brown drop.

It also appears to have allot to do with the circuit they are in. They drive the Vertical circuit nuts.

The symptoms are: poor deflection/linearity, one of the size controls at max, drift/size change with temperature/warmup, poor stability, having to adjust hold controls during warmup

It could just be the supplier rca and pb used in the late 60s. I dont remember running into this with Zenith or other sets.



Sprague made several types of "Orange Drop" capacitors:

PS Series - Film-Paper, and the most widely used by OEMs in TVs.

225P - Polyester Film/Foil
418P - Also a Polyester Film/Foil and widely used by OEM's in TVs.
715P/716P - Polypropylene (may be polyester in lower voltage ratings) - used in higher voltage/pulse apps, as in HV circuits.

SBE now makes all Orange drops, even those for Vishay/Sprague.

There are others (SBE has about 20 types of Orange Drops) but the above were the most widely used in the 50s/60s/70s. It's the PS series that give you headaches - the impregnant gets fully absorbed by the paper, leading to leakage. I've seen "NOS" 6PS-series Spragues with 5 megohms of leakage, and even had a few .0022uf/600V (6PS-D22) caps with flaky epoxy on the ends. 1970's vintage, never used, just went bad in the parts bin. My Sencore LC102 gets some mileage everytime I come across NOS film caps in my parts bin - new doesn't always mean "good". Worse yet, the OEM caps aren't marked to tell what series of orange drops you have.

I had a Setchell Carlson I recapped with NOS Sprague Orange Drops that gave me a fit with sync and AGC. I swapped some of them with CDE caps from Allied and fixed it.

I've never come across a bad "brown" Arco-Elmenco cap, ever. They made film/foil caps with the brown epoxy for Aerovox, GE, and themselves (EM on the cap). Maybe I'm just lucky. RCAs use a ton of these - my CTC16 is full of them, all good.

Cheers,

Thats good news, I have a 16 and it doesn't exhibit any of the problems the sets that must have the PS series caps have.
Im going to cut these open and unroll them for inspection. Im positive they are the ones with paper.

Thanks for the info

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Glad you got the vertical troubles resolved, Dan. I was wondering how the progress on that was going since I talked with you last.

Yea thanks..I was going to shoot you an email on that just been weird with the holiday. Those caps really had my head spinning for a few weeks. I subbed all but one and that one was the magic one..
Now Im trying to do an IF alignment (for practice) and I got a stuck core.