RCA CTC4: the barberized Seville

[miniman82]

Originally Posted by dieseljeep

The CTC5 had two different chassis that year. The better model had a color circuit that was simular to the later chassis.

Yes, you're referring to the differences in the 'Super' and 'Deluxe' chassis. I do admit to liking the circuit with 12AT7's though, pretty nifty.

[mstaton]

The "super"=cheaper, the "deluxe"=better. I have a "super"

[old_tv_nut]

Hi level demods go directly to CRT grids with no further amplifiers.

[miniman82]

Correct. If you look at most other schematics, you'll notice that each color has an output tube. On the 4, the demods go directly to the CRT without passing go or collecting $200. Thus it's high level, where the circuits requiring amplification are considered low level.

[ohohyodafarted]

Tom,

The trim is SOLID brass. It is not plated copper. Brass is acutally COPPER, that is alloyed with zinc. The copper pits or spots you see in the brass finish are areas where the zinc has likely been depleatd from years of chemical corrosion. When that happens the base metal COPPER is what is left and it looks like it was brass plated copper. I can asure you that the trim is solid brass and you can steel wool and scotch brite until you are blue in the face and you will never wear through the plating because it is not plated, it is solid brass. For an easy way to polish solid brass trim follow this link to my web site.

http://antiquetvguy.com/Web%20Pages/...finishing.html

Good Luck,
Bob

[Electronic M]

That is pretty cool Bob! I'll have to try that sometime.


I'm trying to preform the horizontal adjustments and have hit two walls the worst of which is that the linearity coil slug is BADLY frozen (I sprayed some deoxit gold in there and nothing) I'm afraid to proceed because I may end up breaking it. Please help!

Secondly in the HV adjustment procedure it says to adjust the HV control for 25KV, and the most I can get before bottoming out the control is 20KV. Is this something that will shake out if I iterate the procedure a few times?

Putting a meter in place of the HV fuse I'm getting around (ie a little over) 175mA of current.

[miniman82]

Sounds like the output tube isn't being driven hard enough, have you checked the oscillator for correct performance? My CTC-4 will make 25kv no problem, same with the 21-CT-55. They have very stout HV supplies, so if you can't get more than 20 I'd look for issues in the drive or make sure it's not being dragged down somehow. Check that the output has the correct negative grid bias, and make sure the waveform going into it is of the correct amplitude and shape. If that's not it, juggle HV rectifiers till it comes up. I went through 3 of them before mine was stiff enough, just because they are new doesn't mean a whole lot. I've found that color sets in particular are very picky about what rectifier they have in them.

[Electronic M]

Before the first power up I adjusted for the EXACT HOT grid drive voltage called for in sams as a safety precaution. The wave form looked decent, but I did not compare it to the sams at that time.

I just preformed the synchro-guide horizontal adjustment for equal peaks so the drive may have fluctuated, but I seem to recall that the HV was hovering at around 20KV before that so it may not have affected the drive level.

The sam's High Voltage Adjustment procedure is to,with contrast and brightness down, adjust the HV pot for 25KV connect a 0-500mA meeter (I only have a 0-250 unit on hand) across the HV fuse terminals, and adjust the linearity slug for minimum current. Then reset the cont. and bright controls for a raster, and adjust the drive pot until drive bars appear then back off until they are gone.

I was planning to iterate the process until things improved, but I'm hung up at the linearity adjustment because the lin. coil is stuck almost like gremlins have been dumping excess super glue that they have been using elsewhere into the lin coil.

Anyone know how to unstick linearity coil slugs? Even if I skip linearity and go to drive the linearity adjustment will be done in the next step or two and hang me up again then.

[miniman82]

Try a new rectifier before you do anything else, then you can hit the lin coil with a hairdryer set to maximum warp to unfreeze it.

[Electronic M]

Well this sucks!! The damn flat head screw head on the copper adjuster rod for the linearity coil snapped off, but I finally got it loose using a combination of Goof Off poured in the track for the ferrite core and heating the coil by connecting it to 2 flashlight cells thus heating it.

I think I need a new core/copper adjuster rod assembly. Here is what it looks like..


I'll try to see tomorrow if my RCA 9-T-246 has a similar core in one of it's coils that I can scrounge as a replacement for the original core with the destroyed adjuster threading.

Been a lousy day between the rotten stomach bug that ruined my sleep Sunday night as well as making my folks tell me to skip school on Monday, and damaging this part. Ugh.

Edit: all this happened before your post Nick.

[miniman82]

Same thing happened to my CT55, I just turn it with needle nose pliers. It should be possible to file a new slot into it, just be careful. Also, I always wanted to try brazing a knurled knob onto one of those.

[Electronic M]

Thanks for the advise Nick!

My file is a tad large, but if I can get the slug to rotate freely enough I ought to be able to get a screw driver to work with it after filing. I can't comment on the 21-CT-55 layout, but it would be kinda awkward to adjust the linearity control on the CTC-4 with pliers considering they wedged it between the damper and the HV cage. Not what I'd call a particularly good good place for it, but at least it is not as buried as the same adjustment in the CTC-16 (I tend to wear rubber gloves when doing live chassis horizontal adjustments on my 16's as the controls tend to be cramped, and uncomfortably close to dangerous voltages and searingly hot output tubes ).

I'll try some other HV rect. tubes, but doubt they will fare better than what is in there. The tube in there is perhaps the first 3v filament HV rectifier that I've seen that will peg the needle on my tube tester, although I've heard the mantra that the best tester of TV sweep tubes is a TV set.

[miniman82]

What the tester says means squat when it comes to HV rectifiers, unless an open or short is indicated. They simply don't test at a high enough voltage to get reliable results.

[mstaton]

That is so true. I struggled with my 9 with strange HV issues. I could hardly adjust the HV up or down. the regulator and rectifier tested good. I replaced both with NOS and now works great. Tube testers cant always find problems with HV tubes like miniman said.

[Electronic M]

Been back on it for a bit, and here is what has been happening.

After my last post I scrounged a replacement slug from the width coil of my 9-T-246 that seems to be the best thing I have on hand. pictures below.



The HV was (and is still) at 20 KV. The dead IF intermitant that was bugging me devolved into a completely dead IF.
I then got too busy to touch the thing for several weeks.

I got back to it over the week end.

The IF has gone back to intermitantly not working from being dead merely by sitting around. I'm fairly sure this set will need an alignment at some point to work right as color sound and monochrome don't seem to lineup as well as they should.

I did not feel like messing with the IF and HV issues, and instead began tweaking the color circuits. It was hard at first because I did not have a nonmetalic alignment screw driver that was long and slender enough for the dual-core transformer let alone two to tweak both slugs at once. So I went to Radio Shack to see if they had those tools available, and let me tell you that I felt like I was in a grocery store that doesn't stock bread when I was told that those tools haven't been on the shelves for a long time! I ended up making my own alignment tools from some used up mechanical pencils I had laying around from the previous quarter of college which were waiting to be thrown out (good thing I didn't get to that). Shown below are my home made alignment tools.




I have the color adjustments a good deal better than before, but there is still much room for improvement.




Think I'll go at it some more tomorrow......I should really get to bed now.