Soundstage vs background noise?

Tube amps, IME, rarely take a back seat to transistor amps when it comes to soundstage. So I am suspicious that there is something else going on- perhaps related to the noise you are talking about. You might want to test the smaller tubes in the amplifiers- if they are getting weak you could well experience something like this.

A tube power amp might have slightly more noise than a transistor amp, but it should not really be noticeable, since a typical noise figure for any tube amp made in the last 40 years is -95db or better. That's pretty hard to hear on most speakers. So I am thinking there is a good chance your tubes are shot.

The lower noise floor of the new SS amp is now helping to reveal new low level details that were previously masked or blocked by the higher noise floor of your previous Tube gear

The newly revealed details that were there all the time but inaudible due to the masking of the higher noise floor now appear in the presentation as additional Spatial Queues

These additional Spatial Queues help fill in the blanks that were missing with the higher noise floor and the new presentation can have more detail and expanded sound stage because there is more Queues that are audible

Post the tubes that were being used in your old equipment and someone here who knows tubes will comment on if they were low noise or not

If they were not there is a chance a switch to low noise tubes may make the noise floor on the tube amp competitive with the SS amp and bring with it the Tube sound many enjoy
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Tube gear is only as quiet as the tubes used. Lots of variability regarding noise and distortions possible there! It part of the unique charm of tube gear. SS has other noise and distortion issues issues to deal with. Choose your poison. Either can be really good or really bad. Hard to generalize, like most things. Noise is never a good thing though. It obscures other things that might be heard.

Just an addendum to Ralph's post. Not only may the tubes be shot, but if the tube gear is old, it may be time for a recap too. I am a card carrying tube-head. So yeah, tube gear requires a little more care and feeding, but it's kinda fun, gets me involves with the technology a little more and I think sounds nice. Just me.