Telefunkens are known for their durability so they may be chuggin' along just fine. Or there may be a decrease in sound quality that you haven't noticed because it occurred gradually in imperceptible increments.
If you plan on keeping the phono pre you will eventually need new tubes so you might as well get them while you've got time to look for a deal. When you get the new ones plug them in and see if they sound better. When the new ones sound better, it's time to retire the old ones for emergency duty only.
If you plan on keeping the phono pre you will eventually need new tubes so you might as well get them while you've got time to look for a deal. When you get the new ones plug them in and see if they sound better. When the new ones sound better, it's time to retire the old ones for emergency duty only.