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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

Showing 4 responses by gte357s

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. 
gte357s OP
281 posts
 
@rodman99999 i tried turning the screw on top of the 300B, they don’t change the readings.  But I can hear a louder hum if I turn them.

can you elaborate how would the sound be affected by this?  And more importantly, what should I do?  Like buy another tube, or take it to a tech to change the bias?  
gte357s OP
281 posts
 
@rodman99999 
No problem, thank you very much for your input.  
gte357s OP
281 posts
 
those pots on top of the 300B doesn’t change the readings, no matter where the volume is.  
But interestingly, I just try change the 5AR4 on the high reading side, now the readings match, both about 72mA.  I tried switch the left and right of the 5AR4 earlier and the readings doesn’t follow the tube, so I thought the 5AR4 doesn’t matter.  But it seems it has an effect on it.  
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