Hi,   I have a number of vacuum tubes I need to sell, and I was looking for recommendations on where to sell them.  I'd rather sell them as one big lot somewhere, though I realize it might make sense to sell some of the other tubes (Siemens, Telefunken) by themselves.  Are those tubes usable...

Long story short, a family member passed away and I am helping to handle his audio equipment.  Among the items I found a Sennheiser Orpheus, among many other things.   I'm going to be testing it to make sure it's working fine, but is there a US service center for Sennheiser that can handle...