CTC-5 Strathmore!

[roundscreen]

Hi Wirled one.
The coil on the board is the sine coil. The control on the front of the set is the frequency coil. I took a look at my 1v2 and I can see the heater running.
ED

[bgadow]

On mine I had lots of trouble with the video board-the tube socket to the front of the board crumbled & underneath, below the metal shield, there is a terminal strip which turned to crispy critters, killing the raster. Not that this has much to do with yours but worth sharing experiences. I had lots of horizontal trouble but it was nearly all caused by a ham-handed repairman. (guy hangs out in my mirror) I do know that the horiz. hold has a ton of travel in it.

[Whirled One]

Okay, here's a slight puzzler. The horizontal oscillator frequency is still too low, and can't get it in range with the horiz osc coil. Attached is the relevant section of the schematic. As you can see, the osc frequency is primarily determined by L118 (the horiz. freq coil, which also doubles as the customer "Horiz. Hold" control) and C606. This capacitor is a mica cap, and tests fine in my old Heathkit capacitor tester (which can test for leakage at various voltages-- really a handy thing, by the way). I don't have very many replacement mica caps around, but it so happens that I actually had a new 330pF silver mica, so I swapped it in-- but that didn't help. I also tried tacking in a 270pF ceramic (one of the few other high-voltage caps I had in that general capacitance range but lower than 330pF) in place of the 330pF just as an experiment, and indeed it did help slightly, but not nearly enough to get it in range. I don't know the expected resistances or inductances for the horiz frequency coil, as they aren't listed in the RCA service manual I have, so I can't be absolutely sure there isn't something wrong with the coil. It seems like it's within reason, though. I measure 77 ohms between points H and K, and 55 ohms between points J and K. Anyone know the correct values for this coil? I don't have the SAMS folder for it, but it probably has those values listed.

Other things I tried: Swapping the 6CG7 tube had no discernable effect. R606 tested okay, and replacing it with R's of different values had no discernable effect either. C602, C603, R602, and R608 are all okay too.

Any thoughts? I suppose I could "force" it to work by either trying lower-capacitance replacements for C606, or by "padding out" the horiz. freq coil with another coil, but that seems a bit dodgy. Still, it's kinda annoying to be soooooo close to having a watchable picture, but being not *quite* there! :-!

On the other hand, I did stumble on the cause of my overly-green raster. At the back of the CTC-5 "Deluxe" chassis in the area where the chroma section lives, there's a riser board with a number of power resistors on it. Well, there was a cotton-covered connecting wire dressed in such a way that it was practically *wedged* between one of those power resistors and an adjacent tube. Seems that over time, this had scorched the wire, even severing the conductor-- it was so bad that the wire literally *crumbled* at that point when I touched it. Fixing the bad wire got me a much more 'color balanced' raster. BTW, attached is a recent screen image, which also
illustrates the horiz osc problem.

Thanks everyone!

[Steve K]

Replace R608 with a new 100K anyway. That 330 mmf cap replacement should not be a ceramic. Resolder the connections on the entire circuit board as CTC-5s are weak in this regard (also check the ground connections). And as I stated earlier, slightly adjust the sine coil, this may pull it in. I had the same problem on a 5 some time ago and that fixed it.

[yagosaga]

I had trouble with wrong voltages and currents in the horizontal unit too. Read

http://audiokarma.org/forums/showthr...t=30364&page=5

and the following postings. I have renewed all the resistors on the horizontal oscilltor board. Some of these old resistors are crumbly. After renewing I got the correct values. But be careful with soldering. I had a short between grid and screen of the 6CB5 with fatal consequences.
Check R603 too. In my manual it has 150K, not 100K like in yours. In the set I found 90K and changed it with 150K.
BTW: Is A.G.C. ok? The first anode of the 6U8 should have -30 thru -70 volts. (Without signal input 0 volts).

[nasadowsk]

anyone got a whole '5 schematic they could post up here? i was always curious as to what they were like, both the cheapie super version and the better deluxe one....

[old_tv_nut]

http://www.mcmlv.org/Archive/Radio/CTC4.pdf

http://www.mcmlv.org/Archive/Radio/CTC5A.pdf

[roundscreen]

Hi Whirled one.
Go after c610 and c 611- 82 mmf. If they are original caps replace them. Even if they check good. replace them. You can put in 100 mmf caps in there. That should give you good results. Also it would be a good idea to get rid of all wax caps. At some point they will go bad. Looks like you do have a winner. good luck
ED

[nasadowsk]

Interesting - the color section reminds me a bit of the later Zeniths with the beam switch tubes. I wonder if Zenith got the idea from the '5? Also note the cheapie burst wacking the 3.58mhz oscillator.

I guess RCA tried to cut corners a bit too much with the super. Interesting design though...

Hmmm, I wish for a CTC-5 schematic and it appears in .pdf the next day. I wonder if I wish to the schematic fairy for a CTC-7 schjematic, one will appear tomorrow here?

[roundscreen]

Schematic fairy! I needed a good laugh

[old_tv_nut]

The schematic fairy has exhausted all known sources - try St. Clare (patron saint of television)

[Whirled One]

Originally Posted by yagosaga

I had trouble with wrong voltages and currents in the horizontal unit too. Read

http://audiokarma.org/forums/showthr...t=30364&page=5

and the following postings. I have renewed all the resistors on the horizontal oscilltor board. Some of these old resistors are crumbly. After renewing I got the correct values. But be careful with soldering. I had a short between grid and screen of the 6CB5 with fatal consequences.
Check R603 too. In my manual it has 150K, not 100K like in yours. In the set I found 90K and changed it with 150K.
BTW: Is A.G.C. ok? The first anode of the 6U8 should have -30 thru -70 volts. (Without signal input 0 volts).

Say, thanks for pointing all of that out-- I had earlier been following your saga with the CTC-5 Aldrich with interest, but had forgotten that you too had troubles in the horiz osciallator section. I had a few "crumbly" resistors too, though the PC boards appear to be in good shape. Right now, I'm still waiting for some new caps to arrive that I ordered, but should have them in a few days. [BTW, yes, I know that C606 should not be replaced with a ceramic; I only did that as a test to confirm that it would indeed raise the oscillator frequency. Ceramic caps are not stable enough for this sort of timing application...]

Since old_tv_nut posted the schematic for the CTC-5A (through 5H) chassis version (the "Special"/"Super" models), I may as well fill in with the scematic for the CTC-5N (through 5AB) chassis version (the "Deluxe" models) as found in my edition of the RCA manual. Note that the tuner schematic is not included in this diagram.

[oldtvman]

other than the usual maintainence required the ctc 5 produces an excellent picture

[K Urban fan]

Wow that is one of the best sets I have seen to date. It is really in good condition what a good buy!!!

[Whirled One]

Update!

Yes, it's been a while! I sort of put this project on the back burner for a bit, but this weekend I jumped back into it. Ah, well, I figure this set had been sitting inactive for quite a while anyway before I got it, so a few more months won't hurt.

First off, got the horizontal oscillator problem fixed-- it was C602 which goes across the sine coil. It tested okay earlier, but I decided to replace it anyway, and that was it! Yayyyy!

I also decided to just go and re-cap most of the HV section, after C115 "blew" during a test run (this cap couples the 800V B+ boost line with the "horiz tuning" coil in the damper circuit). I'm one of those who tends to avoid blindly replacing caps, but I figure this will save some potential future headaches. ['Sides, if I had just gone and re-capped the horiz osc circuit in the first place, I wouldn't have had this problem for so long! Of course, at least now I know exactly what component was bad, and I learned something in the meantime, so I guess it's a trade off...]

Next I need to tackle the chroma section, which may be interesting, since I haven't had any experience with chroma issues. As you can see in some of the attached images, it was making color for a while [though the color phase or something was way off-- as you can also see, the colors are 'mixed-up', and there was no setting of the hue control that would fully correct them. Also, the fine tuning had to be mistuned (note the noise bands) to get any color]. Unfortunately, it suddenly seemed to "lose" the R-Y channel shortly thereafter. I poked around a bit, and repaired and re-dressed two wires that for some reason had long ago been wedged between the power resistors on the 'riser' card and the adjacent color amp tubes, which had caused the wires to char. However, after replacing the chassis and switching the set on, I find that now there's no chroma at all. I get a passable B&W image (though with poor purity and convergence, since I haven't done anything with that yet), but no color. Adjusting the color killer does not even bring in color 'noise', so there's definitely no color signal getting through.

Any ideas? BTW, one thing I noticed that I thought was odd-- the colorburst crystal in this set is mounted in a glass tube (like a 7-pin minature tube envelope) hidden under a metal shield. I wonder why they didn't use a regular metal-can-mounted crystal in these sets?

Another thing I need to do is clean the tuner. The station selector is *very* touchy at best, and some channel positions don't seem to work at all. I think I'm going to have to completely disassemble the tuner though-- I did try a little tuner cleaner spray in the openings near the switch wafers hoping I could just 'short-cut' this job, but this had little to no effect. Is there any particular "trick" to this?