@viridian
No apology necessary. I’m very appreciative of your input (and clarifications). And I get what you’re stating (and agree) about purchasing based on sound quality, long term reliability and serviceability. That writes and sounds much easier than it is. Not always so easy to make a choice, given the hundreds if not thousands of available choices. Also, it's rather impractical to attempt to listen/audition all options.
Back to nuvistor for a moment, I received a message from Musical Fidelity in response to my inquiry as to where/how the improvement is between the M6si and their nuvista lineup. I don’t know what they mean by "psu", so perhaps you could translate that acronym. Thanks.
The following is from MF:
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The Nu-Vista 600 has the benefit of the Nu-Vista valve preamp stage. The preamp is directly coupled to the input stage so you have shorter signal paths, we have an improved psu over the M6si.
You hear the beauty, warmth and transparency of the valve stage and the transients and power of the transistor power amps.
The Nu-Vista 600 has 4 transistors per channel and outputs 200 wpc, the N800 has 10 transistors per channel and outputs 300w.
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