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 Post subject: Disc Caps..huh?
PostPosted: Jan Wed 03, 2018 4:10 pm 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
I was looking at the parts list on old transceiver and noticed they have some "Disc" capacitors listed as:

5, N150 Disc
22, N220 Disc
25, NPO Disc
22, N75 Disc

The first number makes sense but I don't get what the suffix is for.

I may just replace them even if they are still good because everything in this rig was overheated...big time. I mean, warped plastic components, cracked resistors. Maybe he used it as room heater instead.


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Wed 03, 2018 4:26 pm 
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Temperature coefficient. Not a good idea to replace these caps. The receiver may drift?

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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Wed 03, 2018 4:30 pm 
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Gibson wrote:
I wa

The first number makes sense but I don't get what the suffix is for.
.

temperature coefficient

One random source of info:
https://www.mouser.com/catalog/supplier ... micCap.pdf
See--e.g.---page 5

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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Wed 03, 2018 4:31 pm 
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Norm Leal wrote:
Temperature coefficient. Not a good idea to replace these caps. The receiver may drift?

+1
ceramics normally outlast other components---and the owner of the equipment...;)

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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Wed 03, 2018 8:59 pm 
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Gibson wrote:
5, N150 Disc
22, N220 Disc
25, NPO Disc
22, N75 Disc
Temperature coefficients are used to stabilize the receiver.
They minimize frequency drift with temperature changes.

The tempco is shown as a single letter N for Negative or P for Positive.
That's followed by a number which is the change in parts-per-million per degree C.

So N220 is Negative 220 ppm/degC

NP0 (that's a zero, not a letter O) is stable with temperature changes.

- Leigh

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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 1:38 am 
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Location: Boise, Idaho
Thanks. I was able to do a little reading up during lunch. What I gathered is that an NPO is "outdated" for COG.

I still don't have a great grasp on the whole rating system but understand the basics. It sort of reminds me of my business where we have EER, IEER, SEER , HPLV, COP, HSPF and a few others. In general they all relate to efficiency, just a little differently.

There are some +80-20 in there too. I was just trying to figure out if a straight rated 10% or a Z5U would fit the bill for the +80-20 and those labled as NPO. I'm still not sure and need to read some more.

I know ceramics have a low failure rate, that is not really the issue. I need to do some re-work and some of the leads simply are not long enough to cut them and put them back in so I wanted to have a few spare laying around.


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 3:44 am 
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Gibson wrote:
There are some +80-20 in there too. I was just trying to figure out if a straight rated 10% or a Z5U would fit the bill for the +80-20 and those labled as NPO. I'm still not sure and need to read some more.
Tolerance and temperature coefficient are two different properties.

You can always use a tolerance tighter than the original, like +/-10% replacing +80/-20%.

You should always duplicate the temperature coefficient if at all possible.

As an example, take a simple coil of copper wire with a capacitor connected in parallel. That circuit's resonant frequency will drift with temperature unless a compensating cap is used.

The coil has a tempco of Positive 750 ppm/degC, or P750.
The proper tempco for the capacitor is Negative 750 ppm/degC, or N750.

- Leigh

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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 3:33 pm 
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Yes, I can clearly see the difference as I review the link from Mark and scroll through the selection filters on Mouser.


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 7:20 pm 
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When you run into Zenith ceramic discs you will find about a 95% failure rate.

Dave


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 8:30 pm 
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Do they say Zenith? The only time I have ever ran across a bad ceramic...well it was catastrophic with chunks blow out , so it was obvious, even for me! :D


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 04, 2018 10:51 pm 
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Here is what they look like.
http://antiqueradios.com/forums//viewto ... 9&t=309923

Dave


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 Post subject: Re: Disc Caps..huh?
PostPosted: Jan Thu 11, 2018 6:08 am 
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Gibson wrote:
I know ceramics have a low failure rate, that is not really the issue. I need to do some re-work and some of the leads simply are not long enough to cut them and put them back in so I wanted to have a few spare laying around.

Do you really need to cut them to do the rework? Is there no way to un-solder them?

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