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A blast from the past (2005), The scrapped KSA-50 clone
A blast from the past (2005), The scrapped KSA-50 clone
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Old 29th November 2020, 11:56 AM   #11
kmj is offline kmj  Sweden
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Thanks guys!
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Old 29th November 2020, 02:01 PM   #12
indianajo is online now indianajo  United States
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The worst thing I see about the original device is the lack of finned heat sinks. Too much fan, not enough fins. I think 2 pairs output transistors per channel (which is what I see) needs about a 15 cm x 30 cm heat sink per channel with 6 or more fins to run well without fans, IMHO. If your scrapper has dead variable frequency motor drives, those come with both heat sinks and and enclosure. If you use silicon wafers under the transistors, all four output transistors can be on one heat sink. You can also salvage a flat screen TV, which are full of 5 cm x 12 cm heat sinks. Those already have the transistor pads on them, predrilled. The case can be sawed up and trashed. The screen can be folded up & put in the garbage (use safety glasses & leather or kevlar gloves).
For listening to classical music on 8 ohm speakers I think a 30 v transformer is close to ideal. I'd leave that 1000 va transformer be, it is free. I have a 720 VA transformer in my ST120, I really like that as an amp. Base level on music I listen to in the living room is 1 v pp or 1/8 w, but peaky sounds like piano or drum hits take about 25 v for milliseconds. I prefer 44 v transformers for peaks up to 30 volts. But I listen to grand piano a lot.
I can't imagine living without a decent sound system, personally. I have made speakers out of 6 1/2" drivers with whizzer cones salvaged from projection TV's found on the curb on garbage day. An 8"x8"x14" cardboard box taped shut with the driver screwed to one end and a 1"x1" hole cut in the other has nice bass response, costs about $1 for some screws & zip cord. I put 2 of these in my TV room behind a $25 + $60 new transistors & rail caps PV4 amp, to replace the vile sound of my Sanyo 32" HDTV. Partsexpress has a toslink (soundbar driver) to linelevel converter for about $13.
I've had my entire hifi system + 2500 LP's stolen this September, and I already have a replacement system working. A $4 used FM radio from the charity resale shop, a $30 ebay + $30 freight mma875t mixer (mono), and the speaker from a salvage electronic organ too weird for the thief to carry off have been satisfying my music habit the last month. I listened to the Stevie Nicks concert on the new 32" LG TV last night; sound was severly underwhelming. I need to buy some twisted pair cable and a toslink converter to export the sound over to my mixer/speaker pretty quickly.
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Last edited by indianajo; 29th November 2020 at 02:29 PM.
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Old 29th November 2020, 02:07 PM   #13
kmj is offline kmj  Sweden
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I work at a shipyard and the electrical company next door should get dead variable frequency things every now and then.
I'll check with them.
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Old 29th November 2020, 03:09 PM   #14
jean-paul is offline jean-paul  Netherlands
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Quote:
Originally Posted by duncan2 View Post
I see your pictures show UK standard electrical wiring colours so its either been "built " (terribly ) in the UK of somebody in your area (Sweden ) had access to UK wiring.
Hi that "UK wiring" is EU wiring. In the Netherlands since 1970 to be exact so even far before the EU was found.
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Old 29th November 2020, 04:13 PM   #15
ferret is offline ferret  South Africa
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Quote:
Originally Posted by AudioSan View Post
ferret. How do you figure that 50V caps is to close to comfort? With 30Vac transformer will result in around 39Vdc loaded. +10% margin =43Vdc. Still you are almost 20% below the limit.
Hi AudioSan. I have always been a bit conservative when it comes to PSUs. I prefer to go with a 50% margin, which ends up at 59.5 Volts. Therefore 63 V caps in my book. This also ensures a better lifetime for the caps as they are not stressed too much; and caps this size can be pretty damned costly.

Kevin
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Old 29th November 2020, 06:22 PM   #16
AudioSan is offline AudioSan  Norway
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It's not more stressfull for 50V caps to run at 45V then it is to run it at 35V.
Also, 63V caps is a lot more expensive then 50V caps. And even worse for higher voltage caps.
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Old 29th November 2020, 07:32 PM   #17
kmj is offline kmj  Sweden
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Regarding the caps.
They where brought surplus 2005 and used for at total of a few minutes.
Replace or use?
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Old 29th November 2020, 08:01 PM   #18
AudioSan is offline AudioSan  Norway
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The caps should be okei. But you can measure them to be sure.
There is a lifespan on caps even if they are just stored away.
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Old 29th November 2020, 08:09 PM   #19
kmj is offline kmj  Sweden
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Great, then I know what to work with.
The transistors are TO-3 so depending on the heatsinks I might need to mount them on an anglebar and bolt that to the heatsink.
Is that the normal way to do it or should I consider replacing them as well and omit the anglebar?
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Old 29th November 2020, 08:15 PM   #20
AudioSan is offline AudioSan  Norway
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Yes, anglebar is the normal way to do it. i would use the TO-3's.
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