Some other random thoughts and observations: is this something that settles/goes away with burn in? Is this just the nature of tubes? I also noticed the transformer gives off a slight vibration that seems to coincide with the hum. Normal...?

If it's not being amplified (gets louder with more volume on the pot) then I'm not really sure.  In the past I've had luck moving my ICs away from any electrical outlets.  Proximity to power cords didn't seem to matter, just the wall outlets.

In my experience a lot of times transformer hum is power related. But for sure I'd let the amps burn in for 20+ hours and re-evaluate.

Thanks all for the feedback so far. Letting it burn in seems like the next best thing at this point. I have tried multiple spots/receptacles now with no change. Definitely mostly a left channel thing. It’s there and very low hz in the right, but not nearly as prevalent. Definitely related to the trans. It has picked up slightly in vibration and volume from that point now. Really strange. Letting it stay on for some extended time, with the occasional cool down to cycle between now and Monday. We’ll see. Definitely frustrating. I can tell the sound is out of this world, but the low fly buzz/drone is not acceptable as is. FWIW, listening on Caintuck Betsy diy clones. Source, no source, speaker wires have no effect.

Eldergod,

Pergaps some more burn in will maje a difference, maybe not. Input tube is from Steve? Have you tried another one?

You might want to talk to Steve on Monday if possible.

https://youtu.be/hL8vSHAo0Wk
https://youtu.be/R1TFv50zIYQ
See if these links work. Uploaded a few secs of the trans and speaker to YouTube.

Eldergod,

Steve has a very good article on troubleshooting hum problems posted in the Articles Section.

Your owners manual also has a hum troubleshooting chart.

Is it possible that you have the gain setting set too high somewhere in the signal chain?

Or that the input tube bias is not set properly for your gain setting?

I can make my SE84UFO25 hum through my horns with certain combinations of input tube, bias and gain.

If you have a music store close by that sells guitars, etc. you could get an input tube there.

Update: I’m sorry but I’m getting my tubes mixed up. It is primarily the 12ax7 that guitar amps use.

Eldergod,

If you are comfortable with trying some AC power related testing;

Turn off all of the branch circuit breakers in your AC panel except the branch circuit feeding your audio system.

If the hum disappears, then there may be a problem with one of your other branch circuits or a load connected to them.

Turn the branch circuits back on one at a time until the hum reappears, that will be the branch circuit that has a problem or a load with a problem connected to it.

You mentioned trying a different space ( branch circuit ? ) but if there is a problem somewhere in your other branch circuit wiring or with another connected load, the problem would not be isolated / eliminated.

I do not feel comfortable suggesting any other tests AC power related unless you have extensive experience.

I have 40 plus years in AC power, grounding and bonding in the telco industry.

Maybe your previous amp was more forgiving of an issue that you did not know you had?

Okay, follow up from the weekend.  Tried another powercord, but no difference.  Also tried playing with the electrical branches, but nothing really changed either.  Took the amp, speakers, and my iPad next door to a neighbor's house to try it with no change.  

That all being said, and in the meantime, I was running the unit and burning it in via heat cycling.  While on, I was using it to play quietly as well.  The issue has definitely subsided since Fri night/Saturday.  Probably lessened by approx. 60-70%ish which is good.  I'm able to start enjoying the amp/music now, and feeling less anxious about the issue.  Definitely seems to be transformer related hum/buzz/vibration.  And interestingly enough mainly in the L channel now.  The R is still there but a much lower Hz and barely audible unless I put my ear to that particular side speaker.  I'm curious if anyone else's unit transformer has a slight vibration you can feel if you cup the trans in your hands lightly while turned on?  Also, both speakers (but particularly the L) if I touch the cone while the amp is on (regardless of whether an source is connected or volume level) creates vibrational movement/oscillation which of course is what is producing the audible sound.  I guess I'm asking if your amps do the same where you can feel any energy moving the cone with the amp simply turned on?

Regardless, back to the music for a minute now that I had some time yesterday evening to really dig into it since things are settling down.  I've never really experienced great synergy between and amp and speakers until now.  Listening to tracks of music through this amp and speakers is so different than anything I've encountered.  I can't really even explain it.  Even the lower extension on the Betsy's has so much more presence.  I played Sting's Desert Rose on a whim and was struck by the weight of the bottom end from a full range driver that shouldn't really demonstrate much below 80-100hz.  Not that there was slam there, but I had to check to make sure no sub was connected. The clarity was incredible on my 'test' tracks.  It was like tuning in the radio (showing my age) and hitting that perfect spot where all of a sudden the noise and interference I have been accustom to and normalized was suddenly gone.  Or washing your car in early spring, deciding to also clean the inside of your windshield on a whim, and then driving down the road thinking "Woooowwww..... this is SO much better.  Why have I not done this before?"

Looking forward to more listening this week and next weekend to get more time behind the wheel.

Closing the loop on this in case anyone else has an issue and does a search for something similar.  It's been a few weeks now, and the perceived issue has resolved completely.  I am certain it had to do with the transformer needing time to heat cycle and/or burn-in/season.  There is no audible hum now, and I am able to just sit back and enjoy the music!

Wanted to ask here.

Have 100-200ish hours and a few dozen heat cycles on the amp.  Still hearing hum (through the speakers, 10-20 feet away - quiet, but it is there when no audio is playing).

I have tried a few different tubes (thought not exhaustively), unplugged interconnects, etc. and there is nothing I can do to raise, lower, or change it.  I do hear a hum from the transformer when I put my ear close to it (that hum is NOT distracting and I don't care...unless it is a signal there is an issue there).

I am using these speakers: https://www.madisoundspeakerstore.com/full-range-speaker-kits/fostex-bk-12m-fold...

Almost all of what I am hearing is mid-bass hum from the horn (vs. driver itself, though I can feel the hum if I put my finger on the driver).

I measure 0.01 volts on the speaker posts with no signal vs. <0.001 on other amps...if that means anything.

Archie, here is the thread:

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1621262294

No change to the hum when I unplug the RCA cables.  It seems very 'stable' meaning things like moving cords, moving the amp doesn't make it better or worse.

Thanks,

Ken