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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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14th Mar 2023, 8:34 pm | #1 |
Pentode
Join Date: Jun 2018
Location: Glasgow, Scotland,UK.
Posts: 127
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Smoothing capacitor change / replacement
Hello,
A quick question. I’m restoring a Tandberg Solvsuper 10 receiver. It had in the HT line, one of those 3 capacitors in one can, and one of those within had failed. I have replaced with 3 moderns, but it looks a bit unsightly on the PCB as the hole spacing doesn’t suit. Question is. Can I replace those 3 with just 1 adding to the sum of all 3. There are also 2 1K resistors in the path (see attachment) so what would be best placement for the new single cap placement? Thanks
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Richard |
14th Mar 2023, 8:35 pm | #2 |
Pentode
Join Date: Jun 2018
Location: Glasgow, Scotland,UK.
Posts: 127
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Re: Smoothing capacitor change / replacement
Attachment missing. Ooops
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Richard |
14th Mar 2023, 9:16 pm | #3 |
Heptode
Join Date: Jan 2006
Location: Cornwall, UK.
Posts: 501
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Re: Smoothing capacitor change / replacement
No, you can't replace the three capacitors with one big one as there will always be some ripple with one capacitor. More information here:
https://www.electronics-notes.com/ar...g-circuits.php |
15th Mar 2023, 12:11 am | #4 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,939
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Re: Smoothing capacitor change / replacement
I have a spare Plessey 16/32/32 350V you'd be welcome to FOC.
In old money it is 1.4" diameter and 3" long not counting the tags. Measured C and ESR: 32uF reads 32.3uF ESR 0.61 ohms Second 32uF reads 32.8uF ESR 0.56 ohms 16uF reads 15.5uF ESR 1.29 ohms Which is pretty impressive for a part that was made in April 1964! I'm certainly not in as good shape as I was 59 years ago! I can also give you the clamp, clamp sleeve and insulating pad (to stop the common tag on the bottom shorting to chassis). Anyway let me know if you want it. Craig
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Doomed for a certain term to walk the night |
15th Mar 2023, 12:22 am | #5 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: Smoothing capacitor change / replacement
What you have there is a reservoir capacitor (the right hand 32μF) followed by two stages of R-C smoothing, i.e. two low-pass filters. Ripple will pass preferentially through the capacitors to ground while DC passes only along the resistors. The first filter consists of R240 and the middle capacitor. At 100Hz, the reactance of a 32μF is about 50Ω, so it forms a divider with R240 that attenuates the ripple by a factor of about 21. The same thing happens with R239 and the 16μF, which attenuates it approximately by 11, for a 230:1 reduction in ripple voltage by the time the HT reaches the circuit. In contrast the DC voltage has only been reduced from 295V to 250, a factor of 1.2:1.
To a very rough approximation, to achieve the same result with a single reservoir capacitor it would need to be 230 times as large, i.e. 7400μF, but this would create other problems and is not a feasible solution. |
15th Mar 2023, 11:43 pm | #6 |
Pentode
Join Date: Jun 2018
Location: Glasgow, Scotland,UK.
Posts: 127
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Re: Smoothing capacitor change / replacement
Thanks to all for the info.
I wasn’t sure if what I was thinking was possible. After all why would they do it that way, and now I have the answers. Craig, Thank you very much for the kind offer of your cap. The one I have (original faulty) is about a quarter of an inch smaller in diameter, so I’m not sure it would fit as this is board mounted and not chassis mounted with the can tags going through cuts outs on the PCB. I might just stick with what I have done. I have used good quality and suitably rated Panasonic caps. It’s just that it looks a bit awkward, but otherwise fine.
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Richard |
16th Mar 2023, 11:54 am | #7 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,314
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Re: Smoothing capacitor change / replacement
"Ask Jan First" do some triple capacitors (scroll down). Perhaps your 32+32+16 could be replaced with a triple 20 or perhaps even a 50µF? Diameter is listed as 30mm.
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17th Mar 2023, 8:03 pm | #8 |
Pentode
Join Date: Jun 2018
Location: Glasgow, Scotland,UK.
Posts: 127
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Re: Smoothing capacitor change / replacement
Hi,
Thanks. I’ll look through that. Looks like they stock a lot of interesting parts.👍
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Richard |