Replacing 12AU7 tubes in a Prima Luna Dialogue integrated amp

Yes what tooblue said. You won't hurt anything as they do fit snug. If you start rolling tubes you will become an expert. Just ask me lol. 

Don't swap the same or stock tubes from socket to socket as it will not make any difference. Of course I doubt this is what you meant lol?  If you like the stock power tubes or the tone the EL34 present then you might want to roll in some driver tubes for example like some Cifte 12AU7 in the front 2 slots. These make the MOST difference and Kevin Deal will tell you the same thing. If you want a little more pop or dynamics to the sound then try a power  tube in the KT family such as a KT88/150.  Or even a Gold Lion KT77 which is closer to a EL34 but with more extension and drive. Its kind of like a hybrid tube.  However, enjoy the amp as it is and make sure it is broken in well and your ears to the stock sound and then make an evaluation. One step at a time trust me :)

Before making any decisions I would call Upscale Audio and speak with Kevin or Jarod. Trust me he knows better than anyone PrimaLuna and tubes. Also look at the reviews on his website and that will also help and give you some insight. 

Yes research is good but only you know what your ears like. I didn't care for the KT120's at all.  The 120's had too much glare or upper midrange energy for my tastes. Maybe not your tastes however.  I had no idea you already had KT88's in the amp as it usually comes stock with EL34.  Oh wait I just noticed you have the Dialogue and not the Dialogue Premium so that explains it.  So if you like the KT88 sound then what are you hoping to achieve or want to achieve? Would you like more warmth or maybe more detail?  Mullards will give you warmth and Cifte some detail and openness without any harshness. 

Oh I definitely understand trying something new and didn't realize you were in Australia.  I just couldn't warm up to the 120 at all. Had great bass, drive and separation however, the mids were dry and couldn't tune it out with Mullards. Your mileage may vary but I would look into a Gold Lion KT-88 or the Tung Sol KT150. The 150's tone wise kill the 120 and sound a bit more relaxed like a EL34.  Of course my Dialogue Premium was designed around the EL34 even though it can utilize just about any power tube so your amp may sound better with the 120.  Just read reviews and trust your gut :)

P.S. Andy at Vintage Tube Services does know his tubes also. I dealt with him just a few years ago. Super nice guy. 

Sam

I'm not familiar with any of those tubes but my guess the Gold Lions would be better and not because they are more expensive.  I used to have some Tung Sol 12AX7 and they sounded nice so I would think the 12AU version would also. 

I think you'll notice a difference. Whether it's better only you can decide.