I recently picked up a second-hand Laney LC15R amp and I'd like to change the preamp tubes in it. It currently has three "Ruby" ECC83/12AX7s (and two "Sovtek" EL84 power tubes). I'm not going to change the power tubes for the moment, just the preamp ones.

I know (from reading elsewhere) that my amp has a fixed bias and most probably I'd need to rebias if I changed the power tubes, which would involve opening up the amp and getting to the adjustable trim pot on the board.

However, as I only want to change the preamp tubes, can I just swap them out for any similar type ones? (12AX7s). What if I wanted to use 12AY7s or 12AT7s, could I also just do a straight swap without having to do any rebiasing?

Thanks for any help.
Cathode biased preamp tubes, plug and play! This is true of almost all amps.
The 12AT7 has a higher current so you can rarely see issues, but most often it's a fine replacement for a 12AX7. 12AY7 are a direct swap for 12AX7, no issue there.
Cool, I'm glad I can do a direct swap. I had good results with my last small valve amp by changing the (single) stock 12AX7 for a 12AY7 (and later a 12AT7) so hoping for similar with this one. Thanks.