Groove Tubes Gold Series GT-6550-R Matched Power Tubes Low (1-3 GT Rating) Quartet

I purchased the 6550's 1-3 rating. I've had this amp for close to 20 yrs and had GT's in them and recently switched to try some KT88's. I can't necessarily say the KT88's were bad because in the amp I tried to set the bias but it was max'd and would have had to perform a mod to the amp to match the tubes. So I never heard the potential of the 88's and actually use them for a longer life clean tone and helps playing at lower volume levels. Although when I want to rock, clean or distorted, nothing beats the 6550's hitting the sweet spot with the marshall. I have early Ibanez that just loves distortion and an EJ strat that sounds great with the clean tones. The bias is set for these tubes, they run hot, bet great sound, but realize they will have a shorter life than the 88's, but worth it.

I bought a matched pair for my Marshall JCM 900 50 watt a few years ago and made it sing. I now have a JCM 800 2203 and I'm getting 4 of these for it. Compared to EL34's they have more power for a thicker heavier sound and yet when you roll back on the volume it gets clean like Marshall does. I love these and will never use any other.