About a year or so ago there were several threads going re: using a 6GU5 in place of a 6BZ6 as a RF Amp. in the SP-600 . Has anyone tried it in either an HQ-180 or an HQ-170? If so, was it a direct replacement (after re-peaking the RF stages)what where the results? Thanks, Jim WA8SDF Q. What's the difference between the Cincinnati Bengals and a drum? A. it takes two hands to beat a drum!