Being a manufacturer of tube preamplifier, I can say that we have come across issues with many NOS tubes. Many consumers have contacted us with issues including poor channel balance or poor sound. My first comment is always to install the tubes that came with the unit and report back. In every situation, it was the NOS tube.
With our circuits treating tubes very kindly, we do not have a problem with consumers experimenting with tubes but do recommend they buy from a reliable source that offers refunds or exchanges.
Its unfortunate that today's tubes simply do not have the same sound as many NOS tubes and it is a real gamble when paying top $$ for those golden treasures only to have them go bad within a couple months.
Know your tube dealer and you'll be fine.
With our circuits treating tubes very kindly, we do not have a problem with consumers experimenting with tubes but do recommend they buy from a reliable source that offers refunds or exchanges.
Its unfortunate that today's tubes simply do not have the same sound as many NOS tubes and it is a real gamble when paying top $$ for those golden treasures only to have them go bad within a couple months.
Know your tube dealer and you'll be fine.