[kaleb500]

Hello. I just ordered a La Figaro 339 tube amp. This is the first time I will have a tube amp and I'm quite excited. I went for an OTL for higher impedance headphones.
 
My question is about trying different tubes. How does one know what tubes are compatible? Does the maker of the unit have to provide a list? Or can it be determined from the tubes that it come with (i.e. Tube A in installed, therefore tube B must be compatible)? Or is there some other way?
 
Any guidance or link to similar subject appreciated.
 
Thanks