Change all the 6922 tubes out for a nice set of amperex or mullard 6DJ8 and it will help. You can try to install KT88 in it also but I have never tried that and don't know if that will improve on the SED 6550.
Not sure why people are mentioning 12ax7 tubes. The LP70 uses 6922. I believe the 5751 are a lower gain so be careful.
Not sure why people are mentioning 12ax7 tubes. The LP70 uses 6922. I believe the 5751 are a lower gain so be careful.