#76
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Why do I constantly see folks complaining about the CTC-5 not putting out 25kV when all the original service literature says lower than 25kV for this set is normal? SAMS for early CTC-5 says 22.5kV RCA Original Service Manual says 19.5kV RCA Original Setup Manual says 20kV SAMS for late CTC-5 says 22kV See attached snip-its from some of that literature. Just wondering as I have limited experience with vintage color sets. Thanks.
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-Al Last edited by bigaudioal; 08-25-2016 at 10:48 AM. |
#77
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The problem is not the literature for the chassis, it's the specification itself. Not only did they choose an anode supply for the 5 chassis which only provides around 20kv to the CRT, they also for some unknown reason decided to not make up for that lack of voltage by having ample current reserves. To understand why this is a detriment, see note 3 of this PDF on the 21AXP22: https://frank.pocnet.net/sheets/137/2/21AXP22.pdf ) I say lack of voltage because the 5 is the only one that low, all other chassis (especially the earlier ones) made a full 25kv and had more than enough current in the anode supply to make a full and bright picture without trying very hard. Add this to the fact that the data sheet on the CRT even tells the engineers that less anode voltage equals less brightness, and it will always be a mystery to me why RCA chose in this one particular chassis to do what they did. I don't care to speculate why it happened, it's an issue and makes the 5 a real dog in the brightness department compared to other sets.
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Evolution... |
#78
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The 5s are the BOTB RCA color chassis in my book. If I had a nice 5 with a good 21AXP as well as my beat up 4 with a bad AXP I'd consider the 4 more worthy of the rare AXP.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#79
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Very strange they did that considering the specs and notes on the CRT they were using.
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-Al |
#80
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-Al |
Audiokarma |
#81
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Doesn't this set need to be registered in the ETF's database of surviving CTC-4's?
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) |
#82
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That's why it's the runt of the litter, so to speak. For the same reason I, like Tom said, would cannibalize a 5 to get a CRT for a more deserving set. Done it many times. About the only ones that don't fall into that category for me are the more rare Deluxe doored models like yours, my Wingate and maybe a few others. But apart from that, they fall into the category of donors.
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#83
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Here's a thread talking about the circuit mods, BTW.
http://www.videokarma.org/showthread...=256638&page=2
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Evolution... |
#84
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Thanks very much!!!
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-Al |
#85
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Pulled the chassis tonight. Multiple repairs have been done. You can tell it was owned by a repairman. I have already started recapping the filter caps. More to come later.
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) |
Audiokarma |
#86
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It's amazing what a bit of tarni-shield and elbow grease can do!
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) |
#87
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1) Did the DeLuxe, with its better color, video, and sound circuits, have the same low HV as the Super? If so, that's a shame. 2) If you consider the 5 as a donor anyway, how about the possibility of rebuilding the HV section based on a better design. Maybe the main replacement needed would be only the fly, with the same yoke? Or maybe you'd need both? If this makes sense, I'd be tempted to try it on my 5, which makes me cry because it's got a good CRT being shown to such poor advantage. |
#88
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Wayne,
This is a problem with all 5 chassis, including the Deluxe ones unfortunately. The problem is the flyback, it's got a lot more primary resistance than other models. This means there's a practical limit to how much current the HOT is able to sink, which in turn limits how much HV can be made in the secondary (lower current primary pulses means lower amplitude flyback rectification in turn). I'm not sure why this was done, but it appears to be in the design and intentional. Perhaps the engineers wanted it to be 'safer' or something, we'll likely never know. I have a few different flybacks I can try in my Wingate (CTC-4, CTC-28, CTC-15), but the problem is not getting more HV or a yoke inductance match from the swap- there are ways around both those problems. It's getting all the ancillary circuits to play well with the new transformer that's a big question. None of the tertiary windings that provide pulses to circuits like burst gating or AGC appear to be common across chassis to me, which makes the job of adapting them much harder. Some flybacks had positive going pulses, some negative. Some had very high amplitude AGC, some not. What I see is probably a matching/inverting network and possibly some slight phase shifting to make the new fly work. It won't be a plug in deal unfortunately. BUT- the payoff would be a very nice chassis indeed. The deluxe sets had good circuits in them for color processing, they just had a wimpy horizontal output transformer. I'm going to give it a shot at some point, and I'm also going to try primary side pulse style HV regulation. It'll be like reengineering a complete section of the chassis.
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Evolution... |
#89
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Still have 2 more filter caps to replace, but I thought I'd do a power up to see where I'm at. Current draw is about 2.5A and only putting out about 3 KV. I don't believe the HV readings since the yoke is not plugged in and all I'm using is a piece of wire to short the yoke connection so the HV will actually come up. Found a 80 uf in place of a 40 uf in one of the filter caps and most of the hacked in filter cap replacements had shot their crystallized goo out the side already. Things are going well!
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) |
#90
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Personally I'd pull the H output tube, till the recap is done and the osc. has been dialed in with a scope. Don't want to risk your flyback. On my 4 I did it that way, and when I was ready to install the tube I had it set up to dip the cathode current using the linearity/efficiency slug as soon as I had HV....I pretty much confirmed I had decent sweep and HV then immediately dipped the current. If something is wrong and the fly is being fed too much current, you don't want to run it that way long....We refer to flys for early sets like this as unobtainium for a reason!
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
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