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  #346  
Old 06-11-2015, 09:26 AM
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dtvmcdonald dtvmcdonald is offline
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Another idea: Spend $800, buy the Hallicrafters CTC4 clone McVoy just listed on ebay, spend untold hours working on it, then compare waveforms!

Then you'd have a CTC-4 and a real rarity.
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  #347  
Old 06-11-2015, 10:20 AM
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Originally Posted by dtvmcdonald View Post
Another idea: Spend $800, buy the Hallicrafters CTC4 clone McVoy just listed on ebay, spend untold hours working on it, then compare waveforms!

Then you'd have a CTC-4 and a real rarity.
Yah.... You could do that....... Proly the best way to figure this one out....

.
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  #348  
Old 07-13-2015, 05:30 PM
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I hate to cry Uncle, but I don't think I can take this set any farther without getting it aligned. I contacted the local collector club and asked if they know anyone in the Pacific Northwest who would try that if I delivered the chassis (or the entire TV), but got no response.

When I move the fine tuner, there is a very broad area in the middle of its travel where you bring in a fine B/W picture. You can only get color (true color, if it's a good day, or rolling bars, if it's not) at the opposing extremes of the tuner's range. This occurs on different channels, not only one.

On other sets, I have bypassed the tuner/IF and injected video and audio directly, but injection is not such a simple matter in a CTC-4, if I understood Pete's earlier remarks correctly. I guess I'll wheel this guy out of the shop and work on something else for a while.

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Phil Nelson
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Last edited by Phil Nelson; 07-13-2015 at 05:43 PM.
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  #349  
Old 07-13-2015, 07:35 PM
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Too bad Bob Andersen isn't closer.

http://videokarma.org/attachment.php...hmentid=168681
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  #350  
Old 07-13-2015, 10:01 PM
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Quote:
Originally Posted by Phil Nelson View Post
On other sets, I have bypassed the tuner/IF and injected video and audio directly, but injection is not such a simple matter in a CTC-4, if I understood Pete's earlier remarks correctly.
Phil, the original 1956 RCA construction article for composite video inputs also included two circuits for the CTC4. The second might be the more useful as the other requires a 75-ohm composite signal. The second can be driven by typical consumer equipment composite video outputs, the yellow RCA connectors. The link (notice there are more inductors and caps in this-made-for-the-CTC4 design to develop the requisite curves):

http://antiqueradio.org/art/BROADCAST_NEWS_0656_4.jpg

Pete

Last edited by Pete Deksnis; 07-13-2015 at 10:09 PM.
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  #351  
Old 07-13-2015, 11:20 PM
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Quote:
Originally Posted by Pete Deksnis View Post
Phil, the original 1956 RCA construction article for composite video inputs also included two circuits for the CTC4. The second might be the more useful as the other requires a 75-ohm composite signal. The second can be driven by typical consumer equipment composite video outputs, the yellow RCA connectors. The link (notice there are more inductors and caps in this-made-for-the-CTC4 design to develop the requisite curves):

http://antiqueradio.org/art/BROADCAST_NEWS_0656_4.jpg

Pete
Now this is a tempting solution to my alignment troubles (which are at least as bad as Phil's)! I just found what I think is the correct tuning knob, and cleaned my bench enough to fit it so this may be god telling me to get back to my CTC-4...
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  #352  
Old 07-14-2015, 12:20 AM
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Well, that seems worth a try. At least it would be easier to evaluate the chroma circuits if I knew I was working with a clean input.

Thanks for the tip!

Phil Nelson
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  #353  
Old 07-14-2015, 09:44 AM
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Phil, I think the solution is to learn to do alignments. Its not exactly easy,
but you can do it.

Just one hint: before you do anything else, get a respectable set of
calipers, good to a few thousandths of an inch. Measure and write down
the position of each adjustment. For thinngs that are inside, like hollow cores,
stick a plastic rod into the can and measure how far it sticks out.

That way you can always restore to where it is now.

Get a generator and scope and do it.

A CTC-4 is easy ... except traps, which are set and forget, it has only 5
adjustments for the IF, one per can.
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  #354  
Old 07-14-2015, 12:02 PM
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In the second 21CT-660 preamp schematic from the Broadcast News article, no values are given for the coils L1, L2, L4 and their associated capacitors.

A note says:

L1C1, L2C2, L4C3 -- RCA stock no. 75251

Any guesses as to these values? I don't have references for those part numbers. Presumably each of these was a coil with a cap wired in parallel.

Regarding L3, the note identifies it as "North Hills coil no. 120 I set at 400 mu-h," so I suppose I can use an adjustable coil around that range.

Regards,

Phil Nelson

Last edited by Phil Nelson; 07-14-2015 at 12:43 PM.
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  #355  
Old 07-14-2015, 12:50 PM
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My Merit cross reference shows that the RCA 75251 can be replaced by a Merit TV-151, 4.5MHZ sound trap. It gives no specs though for the part. There are probably Thordarson and Miller replacements as well. Hope this helps.
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  #356  
Old 07-14-2015, 01:16 PM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by dtvmcdonald View Post
...I think the solution is to learn to do alignments. A CTC-4 is easy....
(1) I can't disagree; it's an important skill. But I also think divide-and-conquer troubleshooting is an important tool. Eliminating the RF-IF and detector in this case would neutralize many possible failure points.

(2) In defense of the adapter, before building my first adapter for a CT-100, I reasoned that it was not distorting history because it was RCA who, at the infancy of color television, designed built, and used them.

(3) Phil, I do not have the skill set needed to mathematically determine the missing LC values from CTC4 alignment procedures and the circuit, but I'm hopeful it can be done.

(4) Thanks for the info Tim.

Pete
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  #357  
Old 07-16-2015, 12:57 PM
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I found a source who has two of the three 4.5-MHz sound traps that I would need to build this preamp. In the schematic (below) they are L1C1, L2C2, L4C3.

I am wondering about substituting a modern component for coil L3, which is described as:

"North Hills coil no. 120 I set at 400 mu-h"

I see variable inductors at sources like mouser.com, but I'm not sure what (if anything) might work.

Regards,

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

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  #358  
Old 07-16-2015, 06:23 PM
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dtvmcdonald dtvmcdonald is offline
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The problem is that you don't know if modern or even NOS specified
replacenemt parts are in fact exactly equivalent. In my CTC-100 restoration
I found that for the notorious white coils they were not.
Do you have a scope and sweep generator? If so, you should
play with various parts to get a good result. This will result in you
learning how to sweep and play with parts in a non-stressful
situation.

You are unlikely to find an adjustable 400uH coil in a modern
catalog. Try Playthings of the Past and look in old Miller or Meissner
catalogs to see if they have what you need. A Miller 6195 will work.
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  #359  
Old 07-16-2015, 10:25 PM
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Miller 6195 -- thanks for the tip. PTOP is the outfit that has 4.5-MHz traps in stock. They also have the Miller 6195 coil and they suggested another that might work, so I ordered them both.

Phil Nelson
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  #360  
Old 07-17-2015, 09:40 PM
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Quote:
Originally Posted by Phil Nelson View Post
Miller 6195 -- thanks for the tip. PTOP is the outfit that has 4.5-MHz traps in stock. They also have the Miller 6195 coil and they suggested another that might work, so I ordered them both.

Phil Nelson
Phil, could you please measure the L and C of the traps when you get them?
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