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-   -   Sansui decap problem? (http://www.diyaudio.com/forums/chip-amps/127366-sansui-decap-problem.html)

Taiga 1st August 2008 10:22 AM

Sansui decap problem?
 
Im restoring a good Sansui AU-5500 from 1974. As a part of that will I change all electrolytic capacitors. I have noticed some difference between the scheme and parts list from Sansui. As a bonus there are also difference in what is actually used in the amp. My question to all You clever people is "What on earth mean BRN to describe an el.cap?" Used in the amp is an unknown brand, orange color and marked LR after the value. My guess is that I can use a good panasonic with low ESR (like AK series) but want to know. The caps are used in the pre-section. Sansui has ELNA caps besides these little irritating ones.

As a proof on the loveliness of those old Sansuis. This amp has had its ware counted from the condition it is in. It has never been serviced claims the former owner and despite this, and add the 34 years, the DC 0V and bias current were near perfect.

Kind regards

Nordic 1st August 2008 01:32 PM

Yep sansui's clean up very nicely. Last one I did took a few hours with a toothbrush and a vacuum cleaner. After wich I defluxed the PCBs.

I think as a rule the big black Elna's has given all the service that can be expected from them, and I think even an average modern capacitor will far outperform those other 30 year old lytics. You'd probably have to look for caps of sligtly higher voltage rateing now to get the same pin spaceing as those big old caps...

If the amp is otherwise functional, I would do the changes in small sections, with a good listen in between.

Conrad Hoffman 1st August 2008 02:46 PM

IME, cap life is not easily predicted. I have equipment from the '40s and '50s with perfectly good original electrolytics. I've also had problems with equipment just a few years old. It's foolish to re-cap something that's not having any problems unless you can show that the caps are going bad in capacitance or esr. Build or buy a high frequency esr meter that can check the caps in-situ. It does the PCB no favors to pull good components.

east electronics 1st August 2008 08:02 PM

most sansui i repaired so far
 
and they are quiet many belive me from that time mostly have two types of caps grey and orange .... the grey ones mostly on power sections and orange ones in the tone control mostly signal section

the thing is that when i repair sansui i mostly do total recap meaning that i change the capacitors no matter if the capacitometer says that they are ok ....

grey ones fail after that long time ...orange ones they dont !!!!! i thing they have other kind of manufacture they are better sealed down under diferent mechanical construction otherwise normal elctrolytics

some of them can be replced with mkt also with smal size mostly mods

Taiga 1st August 2008 08:32 PM

Conrad. You are absolute right about dont change whats working. But, and that is a major but, components that is not constructed for eternal life could be a limited factor for what we seek. I look for working capability to produce life to music. When caps are, at least a suspect, to degrade a good amp I change them as I would change a worn stut rod on a car. I checked some caps and about every second had either wrong values or slow readings. When You do not know wich one wrong and wich one is wright You better change them all I think. Still the question is what BRN means to a el.cap.

I have now put the amp together with new caps, mostly panasonic AK series, with polypropylen 0,1 uf bypass, slightly higher capacitance on smothing caps with 4,7 uf and 0,1 uf bypass and schottky diods instead for the existing bridge. IS IT GOOD!!! Now I believe the the descriptions of Sansui early silicon amps sounding like tube amps. Very close detail and high definition. I think grainy is a word for it. Still tight and detailed bass alais not as confident as on my upgraded NAD 3120 or A&R A60. I am happy belive me guys.

DigitalJunkie 2nd August 2008 06:32 AM

I think I did some work on one of those not long ago.New caps on the preamp board,and power amp board,and it was good to go,except for some dirty bias/offset pots,I replaced them with some nice 10turn types,and it's rock-solid. I even managed to get the offset down to like 1mv per channel.
The older Sansui's are very nice amps.Sometimes they need a bit of TLC,but once that's done,they're pretty solid.

There's some more info in this thread:
http://www.diyaudio.com/forums/showt...463#post475463

Nordic 2nd August 2008 08:10 AM

With these old Sansui's you can "hear" the dry caps, I have done two of this year, and agree with the grey caps not being up to standards any more. The sound is dry and anemic with the old caps...

Also the trimpots are not sealed and prone to drifting, I could not believe yours kept their values so well... but will they last another 30 years?

Taiga 2nd August 2008 08:27 AM

Thanks for the tip DigitalJunkie
I use to replace those trimming pots with good multiturn types but with this I managed to find near perfect values with the old ones. Berhapes I go a new round and also replace the resistors in the music path with metalfilm. Thats interesting with the thought that multiturn pots have too small contact area to be reliable in the long run. Sometimes You can do great work with opening the pots and do a good cleaning with isopropyl alcohol. I have done that several times with not too complicated pots with success. I think we overestimate the oxidation problem and the need for all those gastly deoxidazers. There is also the problem with carbon dust from the ware of the surface. Otherwise I should not have the good result from just fysical cleaning I think. The Sansui pots did not look accessible for that so they got a dose with Teslanol Oszillin. That stuff leaves a very thin residue not like some other horror oily ones. Maybe this will be my new rescuing angel. Ill be back in some years to tell...

Great to hear all this work done with the oldies. Have You success with the sound?


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