Green Wagon Posted April 17, 2016 Share Posted April 17, 2016 Sansui AU2900 This is a unit thats previously had all the tone/input and output transistors upgraded. Really neat job, I had to look twice to see 'evidence' of the work done. Came to me with really hideous 'static' noise one channel only. DMM shows the bad channel has a variable output of anything up to 2 volts. Quick chase with spray freezer isolates it to one transistor. Hitting that one the output jumps to 20 odd volts.. Sansui call it an IC - A 2sa798, but in reality its just a pair of transistors in one package. Not a part that exists anymore, so cobbled together a replacement with a pair of matched BC556. Did both channels for uniformity. DC offset is now a bit higher 10mv but thats still better than some amps out there. Best of all, noise be gone....... Also did a quick recap with what I had in stock. Old vs New. 2sa798 and 2x bc556 'bonded' with a drop of superglue before the legs get bent into the right position. 2 Link to comment Share on other sites More sharing options...
Equaliser Posted April 17, 2016 Share Posted April 17, 2016 Good job Nigel! Link to comment Share on other sites More sharing options...
Green Wagon Posted April 17, 2016 Author Share Posted April 17, 2016 Thanks I know I could have asked any of a number of true 'Sui experts here about the 2sa, But why bother them when with a little finger work and using some of my own grey matter will result in a work around. Yes i know there are better replacements out there, but customer budgetary concerns had me finding a usable alternative from what was on hand. Link to comment Share on other sites More sharing options...
skippy124 Posted April 17, 2016 Share Posted April 17, 2016 Hi Nigel, Nice job! Re the 2SA798's - they are avialable locally (WES), I keep a few in stock as these do fail (noisy and/or fluctuating DC offset). The BC pair is a good alternative, I have used BC560C gain matched pairs as an alternative to the 798's. If you ever need some 798's let me know Cheers John 1 Link to comment Share on other sites More sharing options...
Green Wagon Posted April 17, 2016 Author Share Posted April 17, 2016 Thanks John. Ha, didnt even think to check wes. its amazing what rare obsoletes they actually have. Many thanks for the offer. This is the first time in, well, I dont remember when I last needed them. Has to be a decade or more. If I need some, I'll see if I remember wes or your kind offer when it happens 2 Link to comment Share on other sites More sharing options...
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