Nuvista Tubes - General

Gd, I’m sorry, I was not clear. I meant that the tubes used in the MF gear were old stuff, not the design, which I am not familiar with. Just making the point that the designer must source sufficient quantities of a product that hasn’t been made in more than 50 years. Nothing wrong with that IMHO.

You seem to be focused on picking your gear based on the technology involved. I think that’s a slippery slope, and because of system interactions and personal tastes, I generally recommend purchasing based on sound quality, long term reliablility and serviceability. YMMV.

@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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“That writes and sounds much easier than it is.” I’m certainly with you on that one!

PSU is power supply, arguably the heart of every amplifier. 

If you are looking for a rich sound, excellent reliability and serviceability you might have a look at Van Alstine. As you said there are tons of excellent choices out there. I am pre-disposed to gear made in the USA that is very reliable and easy to service. Some really like the marque and some find it lacking in clarity. Rogue also makes a couple of nice hybrid amps but these are class D and I think that you said that you had a technological aversion to that. 

No, directed at all tubes, unless direct output coupled.

I don't believe anyone has made a tube amp/preamp that is direct coupled (no caps or transformers in the signal path) from input to output, like you can with solid state.

The KSS OTL was direct coupled from input to output. You can do it, you just have to jump through some hoops.

I don't think direct coupling is a good idea for either solid state or tubes, because the timing constant of the amplifier goes lower than its power supply. At that point, its possible to modulate the supply, which in turn introduces IM distortion.

We limit the bandwidth of our amps to 1 or 2 Hz for this reason, but we do employ direct coupled inputs and outputs.

George, is your statement about a hybrid being a "sales pitch" in your opinion specific to MF, or in general and applicable to any hybrid amp manufacturer?

I just look at where he used them in the Trivista sacd, that they could be bypassed and probably get better sound/transparency without any circuit design negatives. And that they were maybe from army surplus, and just used to "maybe" give a product more cred/appeal to the "tube set". 

Same what I saw in the MF A3-24 dac a good dac, but two massive power supply chokes (army surplus?) on already very nice super low noise, very stiff low impedance solid state power supplies, what for?? just to make them not stiff again??? Again appeal to some that love chokes in tube equipment?

Cheers George