my experience with the Audionote CD2 and the VTL Deluxe 120 amplifier has confirmed that changing tubes can affect an audible difference.
the CD2 uses a 12 volt tube. it is a 1990's design CD player. I have treid 12AU7, 12AT7, 12AY7, 12AX&, and 5751.
i currently use a GE 5751 black plate.
the VTL uses 12AT7 input tubes. I prefer RCA 12AT7 black plate or 1960's Mullard.
the VTL is a design from the late 1980's.
It is possible that the older tube designs are more sensitive to tube changes, than current production tube products.
Again, i believe the circuit design is key.
Here's another example. I had a Cary AES preamp. I tried many NOS 6SN7 tubes, hardly noticing a difference in performance.
the CD2 uses a 12 volt tube. it is a 1990's design CD player. I have treid 12AU7, 12AT7, 12AY7, 12AX&, and 5751.
i currently use a GE 5751 black plate.
the VTL uses 12AT7 input tubes. I prefer RCA 12AT7 black plate or 1960's Mullard.
the VTL is a design from the late 1980's.
It is possible that the older tube designs are more sensitive to tube changes, than current production tube products.
Again, i believe the circuit design is key.
Here's another example. I had a Cary AES preamp. I tried many NOS 6SN7 tubes, hardly noticing a difference in performance.