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 Post subject: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Sun 10, 2018 3:32 pm 
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Joined: Oct Sun 23, 2011 12:29 am
Posts: 50
Location: Santa Barbara Ca 93109
I am restoring a 1950s Zenith clock radio. Model L520W chassis 5L07
One of the filter caps is a 80uf I do not have but I have a 100uf
Would that work or do I need to spend some of my hard earned money to find a 80uf cap?


Last edited by Dvanwickle on Jun Sun 10, 2018 3:55 pm, edited 1 time in total.

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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Sun 10, 2018 3:48 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
Depends where the cap is located in the circuit.

If it is the first filter cap that is tied directly to the rectifier output, then you should probably stick with the lower-value cap; especially if the rectifier is a tube. This will ensure that the rectifier isn't overstressed at turn-on.

If it is the second filter cap, separated from the first by a resistor, it doesn't much matter if you increase the value from 80 uF to 100 uF. The resistor will provide the rectifier relief from the high surge current possible when applying voltage to a totally discharged large-value cap.


Last edited by lorenz200w on Jun Sun 10, 2018 4:45 pm, edited 1 time in total.

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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Sun 10, 2018 3:57 pm 
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Joined: Dec Wed 25, 2013 7:57 am
Posts: 2317
Location: USA
I found the schematic online.

https://www.tubesandmore.com/schematics ... -corp/l520

As already mentioned, since this is the second capacitor after the rectifier, a somewhat higher value would be fine. Note that a modern equivalent would be 82mfd; you can also connect two capacitors in parallel: 33mfd + 47mfd = 80mfd. Make sure both match or exceed the original voltage rating.


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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Sun 10, 2018 4:27 pm 
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That schematic is drawn differently. Look at dots where lines connect. The 80 mf is actually connected to cathode of the rectifier through a 22 ohm resistor. This resistor will take most of the surge.

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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Sun 10, 2018 5:42 pm 
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Joined: Dec Wed 25, 2013 7:57 am
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Thanks Norm. I'm reminded again not to engage in detailed work before 3rd cup of coffee :)

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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Mon 11, 2018 1:42 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4025
Location: Sunnyvale CA
Dvanwickle wrote:
I am restoring a 1950s Zenith clock radio. Model L520W chassis 5L07
One of the filter caps is a 80uf I do not have but I have a 100uf
Would that work or do I need to spend some of my hard earned money to find a 80uf cap?


Use the 100 mfd capacitor. That is well within the tolerance of the original capacitor (which might have been +100%-50%).

Brett


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 Post subject: Re: Zenith Filter Cap 80uf or 100uf
PostPosted: Jun Thu 14, 2018 4:20 am 
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Joined: Oct Sun 23, 2011 12:29 am
Posts: 50
Location: Santa Barbara Ca 93109
The size of the 100 uf cap that I had was just to big to fit in the small chassis I bought 82 uf cap fit just right.


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