I use the Rx in my Ref 40 and have had no issues. The effect relative to the original rubber type dampers is to give greater control and tightness. You can hear more air and snap in the recording. I have them on all the tubes including the 6550
i did opt for the HAL-O III for my VTL power amps but they run much hotter
i did opt for the HAL-O III for my VTL power amps but they run much hotter