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Old 28th April 2003, 05:51 PM   #1
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Default AC Motor Start Caps for PS use

Has anyone tried to use AC motor start caps for tube amp PS's? For my next amp, I want to avoid using electrolytics, and motor start caps seem to be a reasonable option for high voltage caps in the 10-50 uf range.

Any thoughts?
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Old 28th April 2003, 06:06 PM   #2
SY is offline SY  United States
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Yes, I used some GE-branded ones. It worked just fine.
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Old 28th April 2003, 06:19 PM   #3
EC8010 is offline EC8010  United Kingdom
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Absolutely. They're very handy if you need to tweak the HT voltage by changing the value of reservoir capacitor. They're much cheaper than "audio" polypropylenes.
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Old 28th April 2003, 06:43 PM   #4
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I'll add my "aye".
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Old 28th April 2003, 07:32 PM   #5
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Start caps are crappy, they're made for intermittent use - starting - so they can be really cheap and lossy. You'll probably get better performance with a generic 'lytic.

A run cap, on the other hand, is a quality plastic-film/oil type.

Tim
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Old 28th April 2003, 07:33 PM   #6
dhaen is offline dhaen  Europe
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Default They're OK

Hi,

I have used them in prototypes, and they behaved just fine.
However, I found that the Russian PIO's were actually cheaper. I got those from Guintaras and Tony Welsh.

Cheers,
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Old 28th April 2003, 07:36 PM   #7
dhaen is offline dhaen  Europe
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Default Re: They're OK

Quote:
Originally posted by dhaen
Hi,

I have used them in prototypes, and they behaved just fine.
However, I found that the Russian PIO's were actually cheaper. I got those from Guintaras and Tony Welsh.

Cheers,

Edit:
Having seen Tim's post, the ones I used were called RUN caps.
I'm not at all sure what a START cap is used for
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Old 28th April 2003, 07:58 PM   #8
EC8010 is offline EC8010  United Kingdom
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Bigger induction motors (the sort used in proper lathes, and the like) have a capacitor and starter winding to start them, plus a centrifugal switch once they have reached sufficient speed so that the main windings can safely deliver power.
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Old 29th April 2003, 12:27 AM   #9
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Default JOHN SAN...

Hi,

Quote:
Having seen Tim's post, the ones I used were called RUN caps.
Same, same but same anyway.


John? Hibernation's over.
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Old 29th April 2003, 10:09 AM   #10
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Hi,

Quote:
Start caps are crappy, they're made for intermittent use - starting - so they can be really cheap and lossy. You'll probably get better performance with a generic 'lytic.
Tim,

You're quite right.

The motor "run" types seem better fit for PSU use.

Quote:
Same, same but same anyway.
I was convinced that at one time these were actually the same type, seems that it's definetely not the case anymore.

Sorry about that.

Cheers,
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