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Old 17th February 2019, 04:21 PM   #11
Sandy82579 is offline Sandy82579
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Join Date: Feb 2019
Default Wondering About Components for Mod

So I read this thread with interest since I’m about to put together my TU-8200, and I have a few questions:

I found all of the parts and have ordered them except for the Nichicon CS(M) capacitors. Mouser has them listed in their film capicators but they have no stock and you can’t order them. Digikey doesn’t even have them listed. I substituted the Nichicon UCS series electrolytics. Will those work?

I was also wondering why we shouldn’t use “audio grade” caps (+-10%) instead of “general purpose grade” (+-20%), and would it make any difference?

In addition to twisting the power wire that runs from back to front, would it help to shield it somehow to reduce the hum?

Finally, you cannot get the FETs 2N60Z anymore. No one has them. Do you know a good substitute?

Thanks for going through the mods and providing the changes. I just want to build the best sounding TU-8200 I can,and I think these changes will help.
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Old 18th February 2019, 03:18 PM   #12
paczeltf is offline paczeltf  Hungary
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Join Date: Jan 2018
Location: Budapest
I received this in PM first and replied to that, but now that it has been posted to the thread, here is the summary of what I wrote for those who are interested.

From looking at the respective datasheets, Nichicon CS(M) and UCS are practically identical. You should be fine with either.

I doubt that boutique electrolytic caps would make a big difference in the power supply of this amp, and they also tend to be bigger than regular models. Space is the biggest limitation, unless you want to install these caps to the chassis and connect them to the PCB with wires, which almost certainly will introduce hum.

The biggest reduction in hum was achieved by the bigger C22. Twisting the power wires should be enough, I also recommend twisting the power transformer primary and secondary wires once before connecting them to the respective boards.

I cannot hear any hum with headphones in triode mode (which I do not like), and just a very distant hum in the preferred UL mode, which was not exactly the case with the original setup. The speakers are totally silent in any mode.

If we wanted to reduce the hum even further then we would probably need different PCB layout with separate power transformer secondary windings and grounding for the left and right channels as well as DC heating of the power tubes.

I could not order the FETs online either so I bought 4 pieces from Elekit when a defective "NOS" power tube killed one. Victor may also be able to help. I have not yet managed to find a replacement. The problem here is that Q3 and Q4 are working close to their dissipation limits so we need to be careful here.

Also note that the group of changes that I suggested are kinds of enablers for the driver stage update, which makes the real difference. (This is why I wrote in my post that it was the first part..)

On the other hand, having a more robust power supply with less hum and heater voltages closer to the nominal value should also make a difference.

Regards,
Ferenc
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