DC meter on power amp

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

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?

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.

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. 

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).      

btw:  After you're well acquainted with the amp's presentation, listening to your favorite/most familiar, albums; get one of these and place it atop the power transformer.        Let me know your reaction, if you do.                                                                      I think you'll be surprised and delighted at the improvements it will make.      https://elusivedisc.com/vpi-magic-brick/      The old ones are prettier: https://www.hifishark.com/search?q=VPI+Magic+Bricks:

@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?  

Have you tried turning the tube that reads higher, down to match the other?           Given my unfamiliarity with your amp, and why those pots wouldn’t affect the B+; I’m hesitant to offer further advise.                                                                                                        Perhaps another AudiogoN denizen, can fill in for my ignorance.                                  Personally: I’d run that 300B pair, that read more closely matched, so as to enjoy the amp, until getting gaining further knowledge.                                                                               My suggestion would be: contact Soundgate for directions and information.                       My apologies, for not being able to offer better assistance.

@rodman99999 
No problem, thank you very much for your input.  

Here's hoping your solutions come quickly!

Turn the amps on and turn the volume to ZERO. Wait 10-15 minutes.

Turn the pot that has a HIGHER reading counter clock wise very slowly until it matches the LOWER reading.. BE VERY, accurate..

LOWER is better, HIGHER and HUMMING is NOT..

Contact the manufacture and ask what the bias range is on the pots and recommended setting for your amp and valves.

Normally lower bias setting =  a lot longer valve life. Changes the way they sound when they are cranked up too. 8W. Needs to be right..

Enjoy

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.  

That rectifier is (obviously) faulty.                                                                                                   KUDOS, on your experimentation and discovery!                                                                     The VU readings, still seem a bit high, for a 300B's bias setting.                                             Even if things currently SOUND glorious: I'd advise getting as much info/instruction on the amp, as possible, from Soundgate.                                                                                                      Too much knowledge (regarding one's gear) still isn't enough!