Hi,
I am running a XL-600 right now. It takes 6KM6 and
6KD6 Tubes. Two driving four. Mine talks the best tuned to the Super Mod position. I just re-tubed the amp, all six of them. 24hr Burn in and wow. Im driving it with a Galaxy 2 and half watt Dead-key radio will swing 25. it has been a slow process, in that I was very careful with the duration of key down time on the new glass. Now Im dead keying 600watts with some good forward swing. I have tried repeatedly to lower the dead key and be easy on my tubes. over and over with the sequence to no avail. that would be Plate, Load and Drive. In that order. Over and over, I have tried pulling back the load after peak doesn't matter where i try it. I can tell you this, the tuning stub on the rear of the amp is very important. After i peaked mine I adjusted it, saw another 200watts on Yaesu YS-60 meter. Its a dirty bleeding box but heaven forbid running against one especially a XL-1000. Yall take care, God Bless, Stay safe. Unit415 North Central Florida.