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Acceptable level of hum at max volume?

so i am noticing a faint hum when i set my amp to full volume. not sure if it's been there all along but i was tinkering around and noticed it. here is my setup: rega p3-24 w/ttpsu and herbie mat into jolida jd 9 into decware mini torii. if i switch the mini torii to the second input via the switch i get no hum, but when i switch back to the phono i can hear it. mind you this is at FULL VOLUME. my question is, is there an acceptable level of hum at these outrageous volumes. it's not present in the music at normal or even loud listening levels it's just something i noticed while dickering around. i've tried all the usual solutions to eliminating hum like cheater plugs and moving components and swapping cables. i even have a line conditioner. what say you enthusiasts?
roggae
atmasphere's avatar
atmasphere
7,068 posts
 
Hum is not inherent in tubes even if there is no shielding, any more than in transistor circuits.

However, there are compromises that can occur in a design wherein a slight amount of hum at full volume might show up. I would contact the manufacturer and see if they think it might be normal.
lewm
6,770 posts
 
Actually, I may have overlooked one factor that does differentiate tubes from transistors, and that is with regard to the filament supply. I suppose it is possible, even in an indirectly heated triode, that noise in the filament supply could leak into the cathode, and the AC component might then be amplified as hum. In a well designed tube preamplifier or amplifier input stage, the filament voltage should be fully rectified to DC, with very low AC component, and regulated. If the filament supply circuit is malfunctioning or if there is a "leak" between filament and cathode within a given tube, the result might be a faint hum. In either case, repair is possible. (If the source is a filament to cathode voltage leak, the tube should be discarded and replaced. Perhaps that is what Jburidan experienced.) A competent tech should be able to figure that out.
atmasphere's avatar
atmasphere
7,068 posts
 
If you have regulated filament supplies, even with a cathode/filament short in a tube there is no hum.

One thing have have found though is a lot of tube equipment manufacturers don't know how to ground their gear. I can name a few famous ones off the top of my head. *That* can certainly contribute to hum but also has nothing to do with tubes.
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