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I have been enjoying my TSE with 45 tubes and have not spent much time here. I installed Toshiba 2SK3564 mosfets when building the amp. They were rated higher voltage than a Fairchild I bought at the same time (900v vs 500v).
The toshiba were 15pf typical and the Fairchild were in the low single digits.
There is nothing harsh about the sound of this amp.

Is there any reason to go with a lower crss mosfet? Has anyone done so and found the sound better?
How will the sound be affected?
Is there any reason to go with a lower crss mosfet?

Not ever having built with any toobz myself, I'd hazard that what you'd want to minimize in selecting the FET is any breakthrough from the supply. So Crss is certainly one aspect, but drain output impedance would be another. In bipolar transistors this is strongly linked to 'Early voltage' - the higher, the better.

Not all the Fairchild FETs I've looked at show high drain output impedance - the graphs to look at being those which show how Ids varies with Vds at stepped constant Vg.

<edit> Here's the 2SK2700 which looks textbook perfect below 1A drain current.


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