One thing I am kind of forced to do, if I intend to listen to Christmas carols on this B-1, is go back and forth between the boards as parts come in.
I will be better prepared for the next one, I hope.
 
Okie, so the rear switches cleaned up pretty good, but they were a real PITA to get to

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Cleaned, lubbed and nicely back togheter. I hit the two lytics while I was in there.
 
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some miscellaneous work and the chassis back together. The chassis cleaned up well.
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I took the jewels out of their boxes today and before I put them back, I wanted to share some photos
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I was shocked the first time I saw the size of the SK77s, and I am still shocked to the day. To put things in perspective, here is a lineup next to the usual suspects from Sony and Yamaha:

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some questions and observations:
Has anyone replaced the 22nF ceramic disk caps that sit in the RC network, essentially between the drain and source of the output fets?

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The reason I ask is because the thermal runaway of these things is huge. At room temperature, they test at 20nF on the dot. As soon as the smallest amount of heat is applied their capacitance value swings like crazy. I placed a heat gun on one for a few seconds and it dropped to nearly 1/2 of its rated value. I doubt that the Yamaha engineers have actually intended this.

I did a similar test, with a 10nf silver mica and it does not flinch even after long exposure to heat. Not a blip.

So the question is: Replace or not replace? I do not have 20nf mica on hand but can double up the 10s. They would fit just fine in terms of physical size.
 
Some notes here:
Schematic calls for 2sa673A and for 2sc458s. For the c458s, I found 2sc1571s instead on the board. These are rated as low noise trannies. It looks like Yamaha ended up using something with even better noise floor than the 458s,.
For hFE, the NPNs were in the ~390-430 hFE range, the PNPs were in the mid 100 range. The nice thing about the replacements I used is that I was able to match them for hFE across the line ~430, both, NPNs and PNPs
BTW, has anyone noted the stock for the KSC1845s at the large US retailers??
I suspect these will eventually end up going away..RC still has some on stock in UK...but not for long. They had about 2k in stock. A couple of hundred coming my way.

There are plenty of KSC1845FTA's in stock, aren't they the same?
 
There are plenty of KSC1845FTA's in stock, aren't they the same?
yes they are...
about a week ago they had none..neither did digikey


Edit: Wait, at Mouser, they have ZERO in stock and a bunch on order...same as the other week.
one nice thing about the last batch I got is that they are nearly identical in terms of hFE...all right around 430.
 
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yes they are...
about a week ago they had none..neither did digikey


Edit: Wait, at Mouser, they have ZERO in stock and a bunch on order...same as the other week.
one nice thing about the last batch I got is that they are nearly identical in terms of hFE...all right around 430.

Wow, that went fast. When I was looking they still had 3000 or so in stock :eek:

Looking good!
 
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