Nuvista Tubes - General

I take this to mean your statement about a hybrid being a sales pitch ** is ** specific to MF.

No there are others that do it, just to get the Tube guys interested as well.
Just like McIntosh throw an output transformer on the end of what "could be" perfect good solid state amp, absolutely no need for it if the solid state amp is "done right". Try putting an output transformer on the rear of a Gryphon, Krell, ect, and see what happens to the sound. 
 
Cheers George

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   

what's the point of a hybrid design

Sales pitch, to make one believe there's a a romantic/euphonic side to it. as the tubes are in between the s/s I/V stage and output buffer and serves no purpose, but a sales pitch.

Cheers George 

and is not at all "syrupy." Pretty good for a metal encased micro-tube.

That's because it's got a transistor buffer after the Nuvista to drive the outside world with, without it it'd be "syrupy" if the Nuvista had to do the job.

Cheers George   

George, we will agree to disagree on cap coupling.

That’s why there’s so much rolling goes on with caps as they all have their own coloured sound, the best cap is no cap for the ultimate transparency..

DC management circuitry involved makes it a bit more than no cap.

It's a know fact, that DC servos are much more transparent than cap coupling.


Cheers George

George, please correct me if I am misquoting you - in which case the circuit is no longer pure tube, but hybrid.

Correct, as I was letting the OP know that the final sound signature of it was solid state and not tube.
If it didn’t have the solid state buffer, the sound would be very different and not be able to drive very well either due to high impedance, that why Anthony Michaelson (MF) put the solid state output buffer in it.

Here is a pic of the output section.
https://ibb.co/nvT2sR

Cheers George

Of course there are direct coupled tube amps. The Loftin-White instrumentation amps, designed in 1929, and still used today, were direct coupled designs. The Acrosound Stereo 20-20, designed by the brilliant Ed Laurent, only has an input coupling cap

" The Acrosound Stereo 20-20, designed by the brilliant Ed Laurent, only has an input coupling cap"

This technically should not then be called a direct coupled amp. As there is a cap in the signal path.
It should be described as a capacitor coupled amp with direct coupled output stage.

PS: But wait it’s not even that, it has an output transformer as well, so it has transformer coupled output as well. So in no way can this be called a direct coupled tube amp.

http://www.cma4ch.org/chemo/image/hifi/acrosound-stereo-20-mod-r.jpg

http://2.bp.blogspot.com/-AuRjf-5iXM8/UEYcDrM6X8I/AAAAAAAAAew/RixShlEJghU/s1600/Acrosound_20_20_sche...

Cheers George

To your point about needing to have capacitor or transformer coupling, is this something unique to nuvistors?

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.

Cheers George 

So what’s the down side?

They are a tube, and a tube needs to either have capacitor or transformer coupling, and the best transformer or tube coupling is no transformer or tube coupling.
Unless you go direct coupling with them then there are other pitfalls/compromises that have to be made.

BTW: I believe in the equipment I’ve worked on CDP and DAC, Musical Fidelity never used these tubes without having solid state transistor after them as proper output buffers.

Cheers George

Can you have a look at my question about the Nuvistors in your link

I maybe wrong but I think Anthony Michaelson went to the Nuvsitor when the Trivistor became hard to get, in bulk, or the other way around.

From what I was told by a distributor, he’s known for loitering around military surplus auctions, where he can buy a pallet load of a part for next to nothing, then goes home and designs a specific number of editions using that part.

Cheers George

I also don’t really see DC coupling as a benefit in an amp

That's your opinion, listen to a good direct coupled amp, say Gryphon/Krell ect, then listen to it with the best cap or transformer you can get inserted somewhere in the signal path.

For the most transparent sound, the best cap is no cap, and the best transformer is no transformer.

Cheers George