The 700 volt MM's Non- HRM's like 124..are quickly becoming my favorite... I've used JJ KT77's and Solvtek 5881's... Didn't care much for the Tung sol STR 6L's.. Nice tube just not me!!!
The higher voltage serves up a stronger mid-range.. The added voltage on the plates gives an increased touch sensitivity to the output section as well as increased sustain....Very cool and highly recommended build..(I would never do this as a production amp but have build several custom's..)