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AU-717 Rebuild General Questions

Revisiting this topic now that I've put the amp back together. During cleaning and reapplication of thermal paste I noticed that 1 power transistor had 2 clear insulator sleeves. All had at least 1 insulator sleeve. Was this common? They are very thin clear sheets in addition to the thermal paste.
 
They should all have one mica insulating washer. Unless there is a good reason for it (like washers very thin compared to others), the extra one should be removed. ;)
 
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What is thin? Ie if I measure it with a micrometer is there a thickness which voltage breakdown will cause problems and generate a short?

I'd left it previously under the argument it worked that way. Probably should have removed extra before putting it back together; guess I get to clean it again. At least I marked which one.
 
Crumbs said:
What is thin?
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Compare the thickness of the doubled ones to the singles? But you've installed them now, so unless you plan to run the AU-717 to its limits the importance of ensuring they are all the same thickness is reduced.
 
Crumbs said:
Revisiting this topic now that I've put the amp back together. During cleaning and reapplication of thermal paste I noticed that 1 power transistor had 2 clear insulator sleeves. All had at least 1 insulator sleeve. Was this common? They are very thin clear sheets in addition to the thermal paste.
Click to expand...
I had this with 3-4 mica insulators when I took of the outputs from my AU-D907.
I came to the conclusion that they can split and after 40 years that can happen when you take them of the heatsink. I am not sure about that so I am just going to use new ones. They are not expensive.
 
GrisPato said:
I had this with 3-4 mica insulators when I took of the outputs from my AU-D907.
I came to the conclusion that they can split and after 40 years that can happen when you take them of the heatsink. I am not sure about that so I am just going to use new ones. They are not expensive.
Click to expand...


Splitting may make sense; the layers are not that thick. I'll have to order new mica but for now I'll just use the old ones. It seems to work thanks to all the help from the forum.
 
So I got it together, it worked and then it didn't. Report of status here because I think the issue is specific to my lubrication questions, and presuming the hypothesis is right I strongly advise others to clean everything before reassembly even if it seems to be working.

When it worked pre+amp + amp it is loud and clear. Amp only running off my phone is pretty loud too, but what I noticed is when using the preamp the dB ratings on the knob vs the Yamaha integrated I'd been using with the same speakers. I was at around - 50 dB Yamaha whereas the -52 dB seemed much louder with the Sansui. I'm running the -20 dB down muting switch to get more control, well I was until the other switch noise (current hypothesis) disconnected signal. See report mentioned above if interested in question about cleaning switches, but I'm really looking forward to when it completely works.
 
It may be that the Sansui has a more sensitive input than the Yamaha, so the Sansui may seem louder using the same source, as you may know dB measurements are relative not absolute.
 
Hyperion said:
It may be that the Sansui has a more sensitive input than the Yamaha, so the Sansui may seem louder using the same source, as you may know dB measurements are relative not absolute.
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Input sensitivity makes the most sense, good point. I hadn't looked into it but was just documenting a raw observation.

Even if the dB weren't relative the markings on either amp would still be relative to the reference Resistance used to calculate the values which will not match the speaker resistance except at a few frequencies. I know the Yamaha can do some kind of impedance selection magic to adjust the output path (read more crap in the signal path) which the more analog Sansui could never do.
 
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