Tube Biasing ?

Kitch , Upon checking bias how much has the voltage strayed on your broke in tubes ?

Already broken in tubes stray about 5 mV after 3 weeks or so. I use a somewhat arbitrary number (275 mV) based on an absolute upper limit of 300 mV for the RM-10. After break-in it's more something to do then anything to be concerned about. When new, however, I have had them stray from 275 to over 300 and under 225 after just a few hours. Always wait at least 20 minutes after turn-on so the tubes are warm when you measure.BTW, this applies only to the output EL-84, the inputs, 12ax7 are self-biasing.I imagine the changes are somewhat a function of the design so you need to consult your manufacturer.

Kitch , Have you noticed any sonic difference after calibration ?

There's another thread here on bias vs. sound with some posts from people who I feel are more experienced than I. You all should be warned that I don't hear results from some of the tweaks that are mentioned. Whether it's my ancient ears or my system just isn't resolving enough, who knows? But, Q.E.D., if I hear it, it must be there. Lowering the bias a gross amount, by 1/2, which I tried, gives a "warmer" sound. After a few minutes it becomes clear that the "warmth" is rolled off highs and a general loss of detail and attack transients. I value my RM-10 for the accuracy, detail, and solid bass it conveys while retaining some of the mid-range euphony of tubes. That's the way Rodger designed it and the upper range bias keeps it there.

KITCH , You sound like you've been around the block too , not being talked into the kings new wardrobe . Thank you all for the input with no loss of output and no distortion .