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 7 responses by rodman99999

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!
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.
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:
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).      
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.
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?