12AY7 in a Mesa 400+?

[MK1]

Is it safe to run a 12ay7 in the V1 position of a Mesa 400+? I had one of these laying around and so I decided to try it out it really makes the volume seem a lot more linear and it also lowers the gain significantly so I can run the power tubes a little hotter without blowing the doors of my house. Are there any other tube positions that make a big difference in the tone when changed?

[bassboysam]

Should be safe to use a 12ay7. I like 5751 tubes and pretty much use them in any amp as my v1. You can also try various tubes in v4. That can change the drive character of the power section. V2 can have an impact on the tone stack section but I found those changes to be more subtle.

[AwkwardLoudness]

There would be no problem using a 12AY7 tube in place of a 12AX7. A 12AY7 is specified to have lower gain...about 70% of that in a 12AX7 tube.

[paganjack]

Yeah subbing in the main preamp section will alter the gain structure but should not hurt the amp.
Driver tubes and power tubes must remain within tolerances though.

[Caca de Kick]

The popular swap around here was to run a 12AU7 tube in V4 (furthest away from the input jack). Same result, basically.