Soundstage, layering and tube differences

jim, If you don't know the answer to your question, how will you know that anyone who answers really knows? Go figure.

Anyway, the 'illusion from the harmonic distortion' is related to the difference between solid state devices which typically have odd order distortions and tube devices which have even order distortions. Some feel that even order distortions are additive and odd order distortions are subtractive. You can easily research this issue - it is talked about quite a bit.

Individual tubes differ most audibly in tonal balance (but not exclusively), as do most of the other components in your system. Some are subtractive from the original source but none can be truly additive even if you like the sound better. The pits and grooves are absolute - its what you do with or to them that counts. 

My theory about soundstage is if the musical recording does indeed include the soundstage  "information", then any component in the audio chain - tubes,  cables, source gear, amp, preamp, etc., etc., as well as room acoustics  and speaker placement, can and will contribute to rendering that information. If everything is the same and a change in the tube brand renders a more realistic soundstage, then one could surmise that it's the tube that is delivering more of that information. Don't know if this qualifies as an answer but it's my opinion.

Yes it would be nice if you can change the soundstages,I would think it could help.

,are more 2D? I just replaced my 10 year old SED’s with the Mullards ( which still need burn-in), but they are not nearly as 3D in my amps and are reported to be such.

Yeah there is alot of hype around power tubes.
I can tell you one thing, fair,
the 6550 Svetlana is perhaps the best all around power tube ever made.
Very close is obviously the twin brother to the 6550 , the KT88. , KT90’s are close, thats it,, I do not think 120’s, 150’s match the previous 3 in midrange acoustics.
EL34, kt66,77 can not compete with the 6550/kt88.
russia makes the most reliable 6550/88’s.

Do some tubes resolve the actual recorded room acoustics better or is it a matter of harmonic distortion giving the illusion of soundstaging and 3 dimensionality??

Yes. They are lower distortion, sometimes due to geometry being a bit lower distortion on account of how the electrons flow within the tube, the amount of actual vacuum, how consistent the cathode coating is, stuff like that.

If you like how well EL34s do, triodes can do it even better as they are more linear.