#16
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Maybe skipping the tuner and injecting a signal directly into the video amp and audio amp would improve performance? Also no pesky tuner alignments.
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) |
#17
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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. Last edited by Hagstar; 02-10-2016 at 09:38 PM. |
#18
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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. |
#19
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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.
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#20
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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. |
Audiokarma |
#21
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Well, 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...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 |
#22
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"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. |
#23
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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. |
#24
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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. |
#25
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Phil Nelson |
Audiokarma |
#26
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John H. |
#27
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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. |
#28
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'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.
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#29
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Almost wish I had another CTC-4 to bring back to life. Kevin |
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