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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
1,499 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
6,202 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
6,202 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.
gte357s OP
281 posts
 
It is a custom built Otomon Lab amp.  The builder, Ken, said it is “fixed bias”.  I request to have two meters just because I think they looks cool.  I am actually thinking a VU meter that will move when playing the music, LoL.

http://soundgate.net/product/ODg2.highend

I feel one channel is louder, then I observed the difference in reading. 
rodman99999
6,202 posts
 
One tube has over 10% more B+ than the other, accounting for the difference in balance.                                                                                                                                             "Fixed Bias" means it's adjustable, by you.                                                                                     It appears: there are pots behind the 300Bs.                                                                             Just split the mA, between the tubes, if you like it's current presentation.                       That's a gorgeous piece of equipment (build and looks).      
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