F-2019 transistor isue

[Copanel]

Hello, first of all I want to thank the Audiokarma community for the quality forum content. Through the posts in the exclusive Sansui section I discovered the AU-9500 model, my precious. Two weeks ago there was crackling on the right channel, I connected the CD player directly to the amplifier section and the noise disappeared, so I thought that the source of the noise came from the preamplifier section. After I dismantled the upper cover and the lower one, I sprayed the F-2019 plate receiving transistor spray, the tr-713 transistor reacted to the application of cold spray. I ordered 102 KSA-992 transistors and replaced all six A-726 transistors on this board. My question is, should I also change the other C-1313 transistors on the F-2019 board? Or they can still be left as long as they don't cause trouble.. Now the amplifier works very well, I adjusted the bias current and the output voltage (there were no big differences).

 

[Hyperion]

should I also change the other C-1313 transistors on the F-2019 board? Or they can still be left as long as they don't cause trouble.

There is a possibility that if left in place they will at some point cause problems. There will almost certainly be a performance improvement (reduction in noise most likely), if you do replace them. I like to 'channel match' transistors I replace, but it doesn't matter if you don't do this - I see you have sorted a lot of transistors for gain. By 'channel match', I mean replace each transistor pair i.e. TR705 (Left) & TR706 (Right) on F-2019 with transistors of similar gain, it doesn't need to be exact - just much closer than if done at random).

 

[tutor_turtle]

Hello, first of all I want to thank the Audiokarma community for the quality forum content. Through the posts in the exclusive Sansui section I discovered the AU-9500 model, my precious. Two weeks ago there was crackling on the right channel, I connected the CD player directly to the amplifier section and the noise disappeared, so I thought that the source of the noise came from the preamplifier section. After I dismantled the upper cover and the lower one, I sprayed the F-2019 plate receiving transistor spray, the tr-713 transistor reacted to the application of cold spray. I ordered 102 KSA-992 transistors and replaced all six A-726 transistors on this board. My question is, should I also change the other C-1313 transistors on the F-2019 board? Or they can still be left as long as they don't cause trouble.View attachment 3214066View attachment 3214067View attachment 3214068. Now the amplifier works very well, I adjusted the bias current and the output voltage (there were no big differences).View attachment 3214073

I concur with hyperion, a 50 year-old transistor has a finite life, that and sonic improvements in modern transistors can't be over-stated.
While you're in there, might as well replace some dodgy caps.... ;-)
I did a full boat restoration on my AU-9500 & TU-9500, I couldn't be more happy about it. (Be mindful of the brittle traces while reworking)
Sonic improvements were orders of magnitude increased.
It currently resides as the test mule in my restoration workshop, and otherwise background music while working.
It enjoys more music time than my "home" system.

 

[Copanel]

Thanks for the advice, that's what I'll do. I will be ordering replacements for the C 1313 transistors and a few more resistors found to be out of spec, some capacitors may need to be replaced as well. I sorted the ksa992 transistors because I ordered many and had many to choose from. When ordering more than 100 pieces, the price per piece drops a lot.
Having so many ksa992 I will replace the A726 from the other Sansui amplifiers .