View Full Version : RCA CTC4 Seville Restoration


Hagstar
02-08-2016, 10:57 AM
Well after a year and half of recapping and educating myself I finally am wrapping up this project :huge:. It came with decent purity and I haven't touched the rim magnets around the screen yet., just needs degaussing and a few other touches. Will be taking a more formal video not using an antique mirror soon. This is my first color set. For the last few weeks I was unaware one can't just inject a video signal into this chassis, HUGE contrast and brightness changes once I got the tuner functioning properly yesterday. Most of the noise in the latest ones is my cheap shop DVD player or the camera.

http://hagstar.phanfare.com/7138833

John H.

Phil Nelson
02-08-2016, 12:26 PM
Interesting. Can you give more details about your tuner (what was wrong, what you did to improve it)?

Regards,

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

old_coot88
02-08-2016, 12:40 PM
Hey Ya, John! Hadn't heard from you in ages. :wave:

jsowers
02-08-2016, 02:16 PM
I remember Hagstar from rec.antiques.radio+phono many years ago. That's a newsgroup I've been reading for about 20 years. Ancient history.

Be sure to check out his pictures of the radios at the link he provided. He does very good work.

Hagstar
02-08-2016, 09:17 PM
Interesting. Can you give more details about your tuner (what was wrong, what you did to improve it)?

http://antiqueradio.org/index.html

Well as received the tuner was vexing- it passed the color bars and dots etc. fine BUT was blind and deaf to actual video. For a week or so I failed to read your article and didn't know about the 16 volt video injection thing- results on-screen were muddy from injecting the standard 8 volts, assumed I needed a brightener. Meanwhile I was in the queue here to join. FINALLY I stopped procrastinating and demounted the tuner this past weekend. I took a thin test tube brush and denatured alcohol to the contacts, let them dry and squirted the contact disks sparingly with DeOxit. I also checked the resistors in there. Quite a bit of work getting the cover back into shape- it had been bent up by folks not wanting to take it off. Thanks to the article I did it the right way and suddenly had way too much signal- I still haven't throttled the Blonder Tongue modulator back enough yet.

Thanks everyone, Old Coot especially. He helped me get hooked on this with my first TV, a Crosley from the 2002 AWA Rochester meet which I still have.

John H.

Electronic M
02-08-2016, 09:48 PM
You say there is too much signal. Have you tested the Blonder Tongue modulator on a different known working TV before? If it works right on another TV but over drives the CTC-4 then you need to adjust the AGC control on the CTC-4, NOT dial back the modulator.

Hagstar
02-08-2016, 10:21 PM
You say there is too much signal. Have you tested the Blonder Tongue modulator on a different known working TV before? If it works right on another TV but over drives the CTC-4 then you need to adjust the AGC control on the CTC-4, NOT dial back the modulator.

The AGC control is unable to a handle the full signal well, adjustment was way too critical with 45 db of signal which has to be ten times design.

John H.

Electronic M
02-08-2016, 11:09 PM
Ahh, so you are piping the blonder tongue RF directly into the tuner through coax and a balun....That would cause overload.

I prefer to use my Blonder Tongue modulators as transmitters. With a dipole tuned to the mid band of the channel the 40dBmV ones are capable of ~200' range on most vacant channels, and the 60dBmV ones can do a block radius.

As a fellow CTC-4 Seville owner I'd like to ask you for detailed measurements of the stand/legs portion of your set's cabinet....Mine is missing the stand/legs.

BTW/FYI: dB is a measure of relative signal strength, and without the reference point is meaningless to anything but gain/attenuation. DBmV is a unit of power and is not relative.

Hagstar
02-08-2016, 11:18 PM
BTW/FYI: dB is a measure of relative signal strength, and without the reference point is meaningless to anything but gain/attenuation. DBmV is a unit of power and is not relative.

Yes I am aware of this. In saying 45 db I was referring to the specs and model number of my modulator only, not an accurate power level. I merely intended to give some rough perspective on level.

John H.

Phil Nelson
02-09-2016, 12:30 AM
Well, it sounds like your tuner benefitted from cleaning. I love simple solutions.

If you are getting a strong clear picture with good colors, you may be near the declare-victory point. Some bits in old color roundies are better left alone unless you have a very specific reason.

I was one of those folks using rec.antiques.radio+phono 20 years ago, as well. Learned many things from that group, although I drifted away after web-based forums became more active.

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

Hagstar
02-09-2016, 12:15 PM
If you are getting a strong clear picture with good colors, you may be near the declare-victory point. Some bits in old color roundies are better left alone unless you have a very specific reason.


"First, do no harm." Yes, although I'd love to learn how to use my Triplet sweep generator better I fear the irreplaceable nature of many of these parts, like I have to tell you Phil :sigh:. Now with a CTC9 I'll be more game. I will likely however align the tuner to 2016 standards- to work best on Channel 3 :) At night I wrestle with questions like- if one aligns the tuning for stations which will never exist is it actually aligned? In fact did the alignment even occur?

John H.

old_coot88
02-09-2016, 04:33 PM
Need to be more specific on the word "alignment". Sweep alignment of the IF strip is the very last thing to consider. Alignment of the tuner generally amounts to nothing more than setting the local oscillator so the fine tuning control covers the correct range on each channel.

But since the digital-changeover debacle, all the channels are moot except for the one(s) you want to use.

Hagstar
02-09-2016, 05:47 PM
Well the manual has two pages on tuner alignment, warns you not to touch it without a sweep generator and 'scope. It wants you to match the response curve shown in Figure 46a by adjusting two transformers
and a variable cap. Then check each channel and determine an average expected gain.

old_coot88
02-09-2016, 09:55 PM
I dunno. In some 30+ years in the trade, I never once had to sweep align a tuner. Nearest thing to alignment was setting the LO to the proper channel numbers.

Once in a while, a minor tweak of the mixer plate coil was needed to improve the color passband. The CTC-4's tuner doesn't have a mixer plate coil in the usual sense, though.

A by-the-book tuner sweep alignment would be 'waay overkill unless somebody has twerked with adjustments other than the LO.

You mentioned something to the effect of "being blind and deaf to actual video". Does this mean that with the color control fully off, the display shows no luma (BW video) signal? (With color fully off, normal BW video should still be there.)

Hagstar
02-09-2016, 10:05 PM
You mentioned something to the effect of "being blind and deaf to actual video". Does this mean that with the color control fully off, the display shows no luma (BW video) signal? (With color fully off, normal BW video should still be there.)

Before the tuner began working perfectly after cleaning it was passing just the test generator's signals- all of the patterns. Now it pumps so much into the IF I had to throttle up the AGC a lot.

Oh I tend to agree about sweep alignment. I was just going to examine the curves, I have to bet it's performing fine to judge by the way it's receiving a faint analog image still transmitting on one channel of my cable feed that runs outside near it.

John H.

SwizzyMan
02-10-2016, 04:22 PM
Maybe skipping the tuner and injecting a signal directly into the video amp and audio amp would improve performance? :scratch2: Also no pesky tuner alignments.

Hagstar
02-10-2016, 06:20 PM
Maybe skipping the tuner and injecting a signal directly into the video amp and audio amp would improve performance? :scratch2: Also no pesky tuner alignments.

Actually, no. This requires creating an elaborate jig designed by RCA for this purpose. A 16 volt peak to peak signal with odd rolloff is required. One cannot inject ordinary video into a CTC4 by any means. Phil Nelson in fact is building such a pre-amplifier right now.

I'm not sure folks here are getting my issue is too much gain and adjusting the AGC. There is no more gain to be had most likely but
I talked about alignment as a check- I have no issues to solve I know about. But I know alignment can affect fine detail etc too.

John H.

Penthode
02-11-2016, 01:15 AM
Maybe it is just me. But I do not see the point of this hobby if we do not attempt to restore the set to perform as it did out of the factory. Case in point alignment: I taught myself the process of aligning a TV 50 years ago while in high school. In the late 60's I would find a late 40's set had seen then a lot of service which dictated an IF or tuner response check. It goes without saying what the needs are 50 years on.

In recent years, I have not found a vintage set which has not benefited from at least an IF response check. Every set I have had has always received a cursory IF sweep check even if the picture looked okay to begin with. After alignment I am always rewarded with a better picture, color and sound. Remember that even changing a vacuum tube in the IF strip can noticeably affect alignment.

Proper vintage tv alignment required only a modest investment in time and equipment.

old_coot88
02-11-2016, 03:38 PM
Back in the day, sweep alignment was not part of the routine service paradigm, and was largely neglected. Now that decades have gone by and LC components have (or may have) drifted a tad, sweep alignment is certainly worthwhile to learn to do. But practice on a B&W first.

dtvmcdonald
02-11-2016, 03:51 PM
Maybe it is just me....
In recent years, I have not found a vintage set which has not benefited from at least an IF response check. ... After alignment I am always rewarded with a better picture, color and sound.

I have seen only one old TV that was in what I would call acceptable "factory" IF alignment. Some were truly awful. The exception which was absolutely
perfect in every way, and would have generated a perfect color picture if the video was sent into a CT-100 was my oldest set: a 1939 TRK-12. But its IF is 8-12 MHz. The TRK12 on the other had some rather bad RF alignment channels;
it was not a production set tuner as it was apparently used to test conversion to the "intermediate set" channels.

Phil Nelson
02-11-2016, 05:10 PM
One cannot inject ordinary video into a CTC4Well, yes and no. The required voltage is more in the neighborhood of 2+ volts, not 16 volts, but in any case, a "standard" video signal of approximately 1 volt may not work well in a CTC-4.

Fellow VKer ChrisW6ATV remembered that the Video Drive output from a Sencore VA62A can be set as high as 3 volts, and he got good results from injecting video from that device. (This essentially accomplished what I was trying to do by building a video preamp from the old RCA plans.) I tried that method, and confirmed that it works. More details in this other CTC-4 thread:

http://www.videokarma.org/showthread.php?t=259995&page=25

The Sencore VA62A has a rear jack to accept an external video source, so you can connect, say, your DVD player's video output there and use the VA62A to inject video to the CTC-4. Which is useful for diagnosis, but I doubt you'd want to use such a clumsy setup for everyday watching.

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

Hagstar
02-11-2016, 07:56 PM
Well, yes and no. The required voltage is more in the neighborhood of 2+ volts, not 16 volts,

BUT what about this?

"A signal amplitude of about 16 volts peak to peak sync negative is required for adequate contrast." This is on the schematic as well. All of the muddy low contrast video in my album I posted is from injecting conventional video.

http://antiqueradio.org/art/RCACTC-4VideoRolloff.jpg

John H.

Hagstar
02-11-2016, 08:39 PM
Back in the day, sweep alignment was not part of the routine service paradigm, and was largely neglected. Now that decades have gone by and LC components have (or may have) drifted a tad, sweep alignment is certainly worthwhile to learn to do. But practice on a B&W first.

Looking at the service notes the process looks like several days of work involving lots of unsoldering, lots of resistors to be added and removed, dummy loads, bias voltage supplies with several kinds of bias. I did purchase a digital storage Tektronics 'scope so I can match those precise shapes given in the 'scope illustrations hopefully.

I sure will practice on a simpler set. Every service operation on the CTC-4 involves the possibility of damaging a simple put irreplaceable part. A small mistake and all the work and the set is down the drain. Unlike other folks I have no spares and frankly never see any.

John H.

old_coot88
02-11-2016, 11:28 PM
Jeepers, I sure don't remember anything near that involved. I did use a bias box initially, but found out you get the same results with or without it.
The hookup is purely intuitive and super simple (see attachment). Just tape a turn of wire around the mixer/osc tube as the injection point. Disable the LO by putting the channel selector on a hump between detents. And you're good to go, bias box optional (others' opinions may vary). The procedure is actually fun to do, and you can do it in a morning. Just keep the signal attenuated to the lowest level consistent with good response.

Phil Nelson
02-11-2016, 11:47 PM
"A signal amplitude of about 16 volts peak to peak sync negative is required for adequate contrast." This is on the schematic as well.Hmm, I don't know where they came up with 16 volts. Perhaps I'm looking at the wrong spot on the schematic, but at pin 2 (grid) of the 1st video amp (V110) the RCA schematic calls for +2.7V and Sams calls for +3V (+26V measured from the -23V source).

Phil Nelson

Hagstar
02-12-2016, 04:29 PM
Hmm, I don't know where they came up with 16 volts. Perhaps I'm looking at the wrong spot on the schematic, but at pin 2 (grid) of the 1st video amp (V110) the RCA schematic calls for +2.7V and Sams calls for +3V (+26V measured from the -23V source).

Phil Nelson

I'm thinking I saw that on the 'scope diagrams BUT I might have mis-remembered thinking of this article instead, I had read it back in March after I got raster first time.

John H.

Hagstar
02-12-2016, 04:33 PM
Jeepers, I sure don't remember anything near that involved. I did use a bias box initially, but found out you get the same results with or without it.


WELL that's encouraging, I will recap my Triplit sweep generator very soon then.

They also want you to disable horz. sweep though to remove the flyback derived reference pulse. THEN to compensate for the huge loss of load they show a bank of light bulbs in series or a honking resistor to serve as a dummy load lest the voltage go wild.

John H.

old_coot88
02-12-2016, 05:12 PM
'Oly ell Batman! Maybe get some second (and third) opinions on it then. I never had to disable anything other than the LO in the tuner (and don't know if that was really necessary). Or maybe the CTC-4 actually requires all this extraneous stuff. In any case, do a BW or two first.

stromberg67
02-12-2016, 06:00 PM
WELL that's encouraging, I will recap my Triplit sweep generator very soon then.

They also want you to disable horz. sweep though to remove the flyback derived reference pulse. THEN to compensate for the huge loss of load they show a bank of light bulbs in series or a honking resistor to serve as a dummy load lest the voltage go wild.

John H.

Before I "fired up" the h-sweep in my CTC-4, I cobbled a couple of 100 watt resistors to the proper value and did voltage checks, etc. Worked out as the set came right up with raster upon full power up. Those resistors became super hot after a few minutes and could have roasted hot dogs suspended by strings above them. :D
Almost wish I had another CTC-4 to bring back to life.:yes:
Kevin