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 Post subject: Capacitor ID and replacement type
PostPosted: Sep Wed 22, 2021 1:49 am 
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Joined: Jan Thu 07, 2021 10:41 am
Posts: 87
This 1000pF capacitor on the antenna circuit of my radio needs replacement as it’s double it’s value.
Just wondering what replacement type to use. It’s 1000pF, 1000v DC, 600v AC, 250v AC (b).
Why two values for AC?
Also, what’s the significance of the “K” and the “I”
Looking for advice on replacement type.


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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Wed 22, 2021 1:57 am 
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(b) weird

I'd understand if it had 3 leads and there were two sections A and B

Then it would be two 1000pf caps each rated for differing voltages

But this is strange (to me)

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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Wed 22, 2021 2:14 am 
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The "B" rating is no doubt for a different testing standard than the other voltage rating.

I believe this is an attempt at what we now call a "safety capacitor" which is what I would use to replace it if I were going to. You definitely must use a capacitor with an AC rating.

I also believe the tolerance of the original part was not critical at all in that circuit position and it could have measured that value when it was new, and that there is no reason at all to replace it if it's not leaky.

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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Wed 22, 2021 3:30 pm 
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I assume you have a schematic and depending in it's location in that, we could advise better. Such a high C value would not indicate that the value is critical for a tuned circuit or something. There are a multitude of possible replacements depending on the application. IF it was for coupling or bypass, a film or even ceramic might be sufficient depending on the actual circuit voltages. If it were critical a higher tolerance silver mica or even film type might be indicated. Seeing where it is connected to a coil, that would not immediately imply that the AC rating is of much importance. But without the context of it's function, I cannot confirm that the voltage ratings are or are not important in this case. Some FM table radios in the past have used cap coupling from the AC line to extract signals, as in using the mains wiring as an antenna. In that case it would need special ratings. That would be one cap you would not want to get leaky.

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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Wed 22, 2021 10:11 pm 
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Joined: Jan Thu 07, 2021 10:41 am
Posts: 87
wazz wrote:
I assume you have a schematic and depending in it's location in that, we could advise better. Such a high C value would not indicate that the value is critical for a tuned circuit or something. There are a multitude of possible replacements depending on the application. IF it was for coupling or bypass, a film or even ceramic might be sufficient depending on the actual circuit voltages. If it were critical a higher tolerance silver mica or even film type might be indicated. Seeing where it is connected to a coil, that would not immediately imply that the AC rating is of much importance. But without the context of it's function, I cannot confirm that the voltage ratings are or are not important in this case. Some FM table radios in the past have used cap coupling from the AC line to extract signals, as in using the mains wiring as an antenna. In that case it would need special ratings. That would be one cap you would not want to get leaky.

It’s in the antenna circuit, C27 in the schematic. The same capacitor type is also used at pin 7 of the EL85 valve (C143).


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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Fri 24, 2021 5:20 am 
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Location: near ST Louis Mo 62002
It is a film and foil cap, a polypropalyne cap would be good at 600 volt DC or better would make a perfect replacement , if you have a silver mica that would also work fine in the antenna circuit . In the output circuit for C143 i would use a 1000 to 1500 volt cap in the snubber circuit .

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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Fri 24, 2021 5:44 am 
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Joined: Jan Thu 07, 2021 10:41 am
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battradio@ wrote:
It is a film and foil cap, a polypropalyne cap would be good at 600 volt DC or better would make a perfect replacement , if you have a silver mica that would also work fine in the antenna circuit . In the output circuit for C143 i would use a 1000 to 1500 volt cap in the snubber circuit .

Thanks, would something like this do for the snubber cap?


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 Post subject: Re: Capacitor ID and replacement type
PostPosted: Sep Fri 24, 2021 5:52 am 
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Perfect .

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