New power tubes, bias advise needed.

[guitarguru1969]

Power tubes are drawing an average of 475 plate volts, that tells me according to the webber bias calculator that I should bias the tubes at near 43 ma per tube. This would be @ near 70%. Seems hot to me, maybe because the hottest I have run tubes at has been 38 ma so far. Any advise? Should I just go ahead and turn the sucker up to 42-43 ma per power tube on average? BTW this is a 5150 with a bias mod.

 

[sprack]

70% is a generalized number for safety. I wouldn't go higher than it. Figure out where <= that number you sound best on those tubes and go with it.

 

[Wolfeman]

I wouldn't go higher than 32mA, but that's just my opinion. 44mA is hotter than hell on current production 6L6GC's, and honestly there won't be much benefit over 35mA, you are just going to be killing your power tubes quicker for no reason.

I run around 42mA on my SED's, and they handle it fine. But just be warned that tube life will be cut.

 

[guitarguru1969]

I tried 43 ma and it was real open and burned pretty hot. I dialed back to 32ish and it sounded a little cold or closed to dynamics. I settled on 38 ma for now, seems to be where all of the tubes I have tried end up. I have used matched quads of JJ, Winged C, Ruby, and the original set of unmatched Ruby's. So far JJ's were dark and blanketed in tone. Winged C's sounded real organic and open with lots of creamy tone. The ruby's, both matched and unmatched sounded sharp but slightly open, especially when the bias was turned up passed 35ma or so. I liked the Ruby's when the bias was set towards the 38ma point. Gets me to the slightly creamy and dynamic range but still retains the crisp edge and chug that a 6L6GC is supposed to provide. Now somebody stop me from buying power tubes so I can afford a gallon or two of gasoline!

 

[sprack]

Wolfeman, out of curiosity do you bias with a scope until there's no crossover dist?