When searching for great sounding 6c33c-b (6s33s-v--or the like) power tubes what does one look for? What are the identifying marks that may be on the tube that would help tell me that this is the tube to get. Any idea? I've been cruising fleabay and there are many different types of 6c33c-b tubes out there and I just don't know which to pick. I also visited the Dutch site and it seems that they are out of that tube. Thanks!