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DC meter on power amp

My 300B power amp has two DC (mA) meters.  I know a VU meter moves along with the music, but this DC meters doesn’t.  I realized one has a lower reading caused by the 300B power tube, 0.64 mA and 0.72mA.  I switched left and right, and the lower reading follows.  I tried another pair of tubes and the readings are matched.  Does it mean the lower reading tube needs to be replaced?  What is the effect of one reading is lower?  I bought them used, and they are tested with no leak and shorts, and they are pretty closed in terms of percentage life left.  Would this mismatched in DC reading reflect in a tube tester?

Thank you very much in advance.


gte357s
mattmiller's avatar
mattmiller
1,479 posts
 
Very rarely will tubes be exact. The main thing is, does the tube make noise? Is the tube causing the music to be degraded? Bottom line, if it sounds good then it is good and you shouldnt worry about the tubes so much, enjoy listening.


Matt M
rodman99999
5,981 posts
 
You didn’t specify your amp’s manufacturer.   If those meters are there, for you to determine bias settings: that typically indicates, you’re able to adjust them.   Look for pots labeled, "BIAS" or, "B+", externally, on the amp.                                                                                                                Do you have a manual?
rodman99999
5,981 posts
 
Plate current for the 300B is typically around 60mA, but that can vary, depending on the tube (and/or amp) manufacturer’s recommendations.                                                 Please, provide more info, regarding the manufacturer and model, of your amp.                If you don't have a manual: there's probably one available, online.
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