Speaker Placement Nirvana

Grimace,
I do not know exactly what was happening - my guess is that @ 4' from the wall behind the speakers, speaker must have been in a peak node of a bass standing wave (all rooms have standing waves & their freq differs based on their/room dimensions) which caused that freq to be enhanced creating a boominess.
I *assumed* that your ceiling height is 8' & calculated the standing waves for your room. The axial modes are most powerful. Axial modes involve floor-ceiling, both long walls, both short walls i.e. any 2 parallel surfaces. I found that the floor-ceiling standing wave freq is 70.625Hz. Using speed of sound = 1130ft/sec, the wavelength of 70.625Hz is 16'. So, a quarter wave of 70.625Hz = 4'. So, if your speaker was 4' from the wall behind the speaker, you must/could have been at the peak of the 70.625Hz wave & that bass freq got enhanced creating the boominess.
Also, a tube amp, in general, does not have low enough output impedance (just the nature of tubes) to control the bass well to begin with. So, any room impairments could easily overwhelm such an amplifier.

Congrats,
You've just changed your Mustang for Schwinn. Certainly lower emission, healthier but substantially slower:-)

Room effects may somehow tweak this problem but not resolve. I believe the previous and further posters would agree.

I think Grimace has experienced what I have: changing the position of the speakers in the room absolutely swamps changes to electronics, cables, etc.

Marakanetz, I'm not sure I understand your comments. If you'd care to, perhaps you could be more direct in what you're saying. I'd be interested to know. It seems that Grimace did "resolve" his "problem." So I'm not sure what you meant. Thanks.
-Bob

Mustang is Ford Mustang, a muscle car.
Schwinn is famous bicycle manufacturer.
I don't think that Grimace solved his problem since he does need current. Changing speaker position is only tweek(valuable I admit).