I just got a weber biasrite tool..and a new matched set of GT kt 66 HP's (rating 4) ......When I tested them in the RT 66, the bias was slightly different for each tube when I used the AB switcher...........is this normal for matched tubes? Initially and prior to changing the bias, One tube hovered around 31.5 mA and the other around 33.0 mA...as I adjusted the bias, they maintained this differential..........
I am completely new at servicing my own equiptment so I am not sure what the tolerance is for matched tubes........how matched is matched in mA's? Do they have to be exact?
my amp tech, a bit old school, but still makes jt45 and deluxe reverbs and supers for people and repairs amps etc.. been at it a long time , made this comment when i bought and had him bias a new set of groove tube E34Ls #6 to be biased at 36 ma : "when i biased one of the tubes at 36 the other one whould come in at only 33..it should be as close as "2" if they are professionally matched.." but the amp sounds great, hah.
thanks fellas...........I kinda had a feeling that was gonna be the case, but I wanted to make sure for future reference. My ears are telling me everythings fine! My Rt 66 has that BIG "GROWL" again win pushed with humbuckers..........nuthin' like a fresh set "o" tubes!
This is very normal but you also have to remember that what you are measuring is static match at idle. You want to stay with 20% or else you can have hum issues, but on tubes which are dynamically matched rather than statically matched, when you look at the amp on a scope you will see dynamically matched tube be exactly matched. This is generally not the case with tubes which are simply static matched. But ... to dynamically match tubes takes about $400,000 worth of equipment and this may be a bit outside of the reach of most tube vendors.
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