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  #31  
Old 06-24-2017, 10:34 AM
old_coot88 old_coot88 is offline
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Originally Posted by Crist Rigott View Post

Any idea why this was done?
The only effect of adding that cap would be a slight increase in bass response.
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  #32  
Old 06-24-2017, 12:22 PM
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Originally Posted by jr_tech View Post
Looks like an attempt to "improve" the audio, by increasing the low frequency response. Mine did not have the added cap... perhaps it was added later by a serviceman. Nothing critical there, I would just use ceramic caps to replicate the circuit.

jr
On the other hand, the 1 meg resistor and the 820 k resistor on the board should 5% tolerances or better, because they set the grid bias on the audio output tube.

jr
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  #33  
Old 06-24-2017, 02:19 PM
Crist Rigott Crist Rigott is offline
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OK, I have decided that I probably will make all new couplates or networks. Not sure of the right name.

My biggest question is what voltage should the ceramic caps be. I've checked with Mouser and it looks like some caps I can only get like 100 volts while most I can get 630 volt or more.

I believe that these are very similar to what the Predicta uses.

Here is a link to a 24x36 schematic which shows all the couplates.

Thank you.

https://www.dropbox.com/s/j2ww1hzzva...24x36.pdf?dl=0
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  #34  
Old 06-24-2017, 05:28 PM
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Check out this predicta thread, starting about here:

http://www.videokarma.org/showthread...=255328&page=3

jr
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  #35  
Old 06-24-2017, 06:23 PM
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Quote:
Originally Posted by Crist Rigott View Post
OK, I have decided that I probably will make all new couplates or networks. Not sure of the right name.

My biggest question is what voltage should the ceramic caps be. I've checked with Mouser and it looks like some caps I can only get like 100 volts while most I can get 630 volt or more.
That's a good question. The 100V would probably be smaller and so easier to fit, but some places would definitely require something higher. The grid of the horizontal output is one place I'd use a higher voltage rating because of the large AC signal.
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  #36  
Old 06-24-2017, 10:53 PM
Crist Rigott Crist Rigott is offline
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OK guys I'm at wits end. I'm trying to pick out the caps that I need for the couplets. I know for K5 the 1500pf cap needs to be 1KV for sure. But the rest of the caps I'm trying to pick out I can get some at 630v and some only at 100 volts. Maybe I'm over thinking this but this is gotten to be ridiculous for me. I've spent the better part of today going through lists of caps that Mouser has. I'm drowning in datasheets. This shouldn't be this difficult.

Can somebody let me know what they used when they did their couplets? It would be appreciated.

Last edited by Crist Rigott; 06-27-2017 at 02:03 PM.
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  #37  
Old 06-24-2017, 11:14 PM
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What value caps can you only get in 100 volt rating? Perhaps a slightly different value cap with a higher voltage rating can be substituted, or perhaps we can figure out if a higher voltage rating is actually need where the caps are used.

jr
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  #38  
Old 06-25-2017, 11:03 AM
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Notimetolooz Notimetolooz is offline
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Quote:
Originally Posted by Crist Rigott View Post
OK guys I'm at wits end. I'm trying to pick out the caps that I need for the couplets. I know for K5 the 1500pf cap needs to be 1KV for sure. But the rest of the caps I'm trying to pick out I can get some at 630v and some only at 100 volts. Maybe I'm over thinking this but this is gotten to be ridiculous for me. I've spent the better part of today going through lists of caps that Mouse has. I'm drowning in datasheets. This shouldn't be this difficult.

Can somebody let me know what they used when they did their couplets? It would be appreciated.
Is the difficulty because you are trying to stick to ceramic? I think that if you have to that film would be OK. Also the values used in the networks seem to be non-standard values in many places, I wouldn't be too concerned about an exact match.
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  #39  
Old 06-25-2017, 12:15 PM
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Perhaps a kit of 2kv caps like this offering from 'zon will get you close enough. I find that a little sorting with a decent meter will often find "in between" values.

https://www.amazon.com/dp/B00DDJQAAO?psc=1

How would one substitute the distributed cap in k-4... multiple caps and resistors? Perhaps 3 27k or 33k in series with 4 1000 uuf caps to ground.


not affiliated,
jr

Last edited by jr_tech; 06-25-2017 at 12:22 PM.
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  #40  
Old 06-25-2017, 01:54 PM
Crist Rigott Crist Rigott is offline
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Guys,
I appreciate your comments. After a good night's rest and a clear head I have selected all 630V TDK caps with 2 exceptions. 1 is the 1KV 1500pf cap used in K5 the Vertical Feedback couplet, and the 82pf cap used in K6 the Horizontal AFC couplet. The 82pf cap that I could find was a TDK 100V or a Kemet at 200V. I know I could always use a mica cap. BTW, all the caps are ceramic MLCC's and COG/NPO type.

Here's a link of the typical TDK cap that I'll be using:
https://www.digikey.com/product-deta...0-1-ND/5812015

Last edited by Crist Rigott; 06-27-2017 at 02:27 PM.
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  #41  
Old 06-25-2017, 02:07 PM
Crist Rigott Crist Rigott is offline
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This leads me to another question. I couldn't get a 200pf cap used in K6 the H. AFC couplet. So I'm guessing that a 220pf would work?

Also the 5000pf caps used in K1 Blanking, K6 Vertical Integrator, and K8 the CRT Isolation couplets will be replaced with 4700pf caps.

Also the 8000pf caps used in K2 Audio, and K3 Sync Coupling couplets will be replaced with a 8200pf cap.

Anybody see any problems with those subs?

Thanks.

Last edited by Crist Rigott; 06-25-2017 at 06:08 PM. Reason: Changed 200pf to 220pf
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  #42  
Old 06-25-2017, 05:45 PM
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If you mean 220pf as a substitute for the 200 in the first sentence, then yes, all of the substitutions should be fine (all within 10% of the desired value).... I suspect the original parts are 20% anyway.
Are you going to be using the set with a VCR? Most older sets do not do well with a signal from a VCR because the horizontal AFC is too slow (causes flagging of the top of the picture) reducing the 200pf to 150 or so, possibly could help if this is a problem.

jr
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  #43  
Old 06-25-2017, 06:06 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post
If you mean 220pf as a substitute for the 200 in the first sentence, then yes, all of the substitutions should be fine (all within 10% of the desired value).... I suspect the original parts are 20% anyway.
Are you going to be using the set with a VCR? Most older sets do not do well with a signal from a VCR because the horizontal AFC is too slow (causes flagging of the top of the picture) reducing the 200pf to 150 or so, possibly could help if this is a problem.

jr
Yes, I corrected my post. Typically I don't use a VCR. Maybe I should use a 180pf instead of a 220pf just in case?
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  #44  
Old 06-25-2017, 07:26 PM
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I just looked at some old notes and now think that c 39 is the likely candidate to change to decrease the horiz AFC time constant.

jr
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  #45  
Old 06-25-2017, 10:40 PM
Crist Rigott Crist Rigott is offline
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Originally Posted by jr_tech View Post
I just looked at some old notes and now think that c 39 is the likely candidate to change to decrease the horiz AFC time constant.

jr
OK. I'll go with the 220pf cap.

Another question. Do you think that for the 1500pf 1KV NPO cap used in K5 the Vertical Feedback couplet I can use a SMD? The package is 1812 and I can solder leads on it or just solder it to my pcb boards that I'm designing?
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