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Recapping an Altec 1589b

 
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A.David.MacKinnon
mixes from purgatory


Joined: 07 May 2003
Posts: 2907
Location: Toronto

PostPosted: Thu Jan 19, 2017 10:37 am    Post subject: Recapping an Altec 1589b Reply with quote

I've got an old Altec 1589b that's got some nasty hum on the output. The hum is consistent regardless of what the input settings are so I'm guessing it's the output section and/or the PS. It's ancient and has never been recapped so I'm sure it's time. The problem is that I can't find caps that match what's in there now. The filter caps are 150uf 35v and I can only find 160uf (or something along those lines). same goes for the smaller electrolytics in the output section.

Am I safe to replace caps with new ones of slightly higher value (both uf and voltage)? Should I go for the closest higher value?
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floid
re-cappin' neve


Joined: 03 Jan 2006
Posts: 736
Location: in exile

PostPosted: Thu Jan 19, 2017 12:29 pm    Post subject: Re: Recapping an Altec 1589b Reply with quote

Most electrolytics are +/- 20% anyway, it shouldn't be an issue. If it's in the p.s., I'd probably bump those 150uF caps up to 220, actually. Use 4.7 for 5uF, .022 for .02 etc. since it's really just a labelling thing - look up how to calculate an RC network and you'll see what I mean, the numbers stay virtually the same and well within the mfg tolerance.
The problem i've run into before is trying to use an electrolytic with too high a voltage rating - say there's several 4.7uF caps in the circuit, but with voltage ratings ranging from 5v up to 50v. It's tempting to order 20 4.7/50's to get the price break, but a 4.7/50 may not function properly in a spot where it receives a 3v polarizing voltage and ends up behaving as a much smaller cap (= poor bass, odd timing speed, etc). The datasheets usually say it's okay to substitute a higher voltage for a lower one, but there are practical limits.
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A.David.MacKinnon
mixes from purgatory


Joined: 07 May 2003
Posts: 2907
Location: Toronto

PostPosted: Fri Jan 20, 2017 3:06 pm    Post subject: Re: Recapping an Altec 1589b Reply with quote

Awesome. Thanks for this. I'll stick as close as I can to the voltage ratings. I have a local supplier so I usually just get what I need and never bother with bulk discounts anyway.
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