s,

I'd just like to relate that the one time I thought I had a real hum isolated to one of my Decware amps. . .the real culprit was an unshielded interconnect that was routed just right (or just wrongly) to develop a hum in the system. If you're using unshielded interconnects, have they been moved even a bit lately?

That is quite the thread and I have to tell you I had this urge to start giggling to myself upon seeing how others can get caught up in trying to resolve an issue.   I've definitely been there and wondered at times if I am just over the top so its always reassuring on some level to see others grappling with the HUM god.  lol.   Nope.  use all shielded cables Lon.  That thread though did not contain the post where by someone mentioned sending his Taboo  (i think) back in for recap.  Which reminds me.  bad caps usually cause hum at the speaker and not the amp itself If I recall correctly.   I have taken various units out of my system over the years because of transformer hum and usually its quite noticeable that it is actually emanating from the tranny.  I just laid my ear on that hot tranny and avoided burning my nose on that glowing telefunken and yep.. praise the el84 it would appear to be  mechanical hum.  
I have a the sleeper Sony ST J75 that had horrible tranny hum and Mark from Absolute Sound Labs did an overall on that tuner for no cost as sort of a promotion I guess and he also heard me venting on the tuner forum about a raw deal that I got on it and he sent that tranny out to a shop somewhere back east and lo and behold..  That J75 is a stealth tuner now.   It would have been a 500 dollar restoration which I did not have to pay but gave him some money for parts and now of course I dont want to sell the tuner because with all that work in it it makes it a keeper --would never get much for it.   Transformers are often the culprit for hum coming from the amp itself --bad caps would show up at the speaker.  

Oh, I think it is the tranny.  put my ear to it ..  What potentially can happen is there is vibration of the plates. What exactly causes some to have an audible vibration and some not I suppose has to do with varied factors which I have some knowledge of but certainly not qualified to say exactly what in this case.   On some level a small amount I think can be considered normal but then why do preamps generally run dead quiet?  Like the Csp2 I have sitting next to the Taboo.    Just depends on how noticeable , system set up, etc.    tightened the transformer screws  a bit and they are fine and  the rectifier tube is unlikely problematic   A  Bendix military 5y3gt equivalent.  Here's an interesting link on the 6106 missile tube.   http://www.radiomuseum.org/tubes/tube_6106.html    If anyone has a lead on a pair of speakers for sale..  Any Decware as long as they have passives in addition to the drivers of course I may be interested.   I find my MG 944's to be fantastic speakers and will never part with them.   I have had the early cylinder speakers--- model escapes me at the moment.   1.5 radials maybe.      
And actually to be clear on the  hum  --it cant really be noticed with music on although perhaps at night on quiet passages as system sits closer to listening position than the speakers.   Perhaps I am being just more persnickety now I that I have just retired and have all this time on my hands that I need to occupy.    [smiley=cheesy.gif]

that is interesting.  I will try it for sure.    [smiley=beer.gif]  curious as to why smiley does not work now.      worked that time.  [smiley=2vrolijk_08.gif]