Thanks everyone. Particulary the recent article comparing 6550's sound interesting. My guess is that I have 1,000 to 2,000 hours after 20 years. I did not count. Recently listening as much as 10 hours per month. My voltages are very high 620 Volt. My repair shop said this makes it much harder to find a tube that will last. He said the Tung Sol are not very good with high voltage.
How to pick which brand of 6550 tubes to purchase
I have a pair of Ray Lumley M-100 amps. Have used two complete sets GE 6550 for close to twenty years. Need new tubes. Which tubes would you recommend to purchase? Any knowledge of the sound character of the different models. I like the accurate/neutral type of sound versus the too valve sound.