Thanks for the reply Paul. Loose screws (besides mine) occurred to me too. In fact, after the unit cooled down during the power outage I pulled the plugs and retightened all the screws. (I painted the chassis and bell cap with USA hardware paint. This paint seems to reach final cure slowly or is naturally soft. Anyway, the screw heads appeared to be slowly deforming the paint i.e. pushing the paint out from underneath the screw heads.)
I had not checked the sound before the power outage, but after an additional 24 hours, the net result was that the hum hadn’t changed or was possibly lower in level. What had changed was that tapping most anywhere including the small tube (oddly, an exception is the bell cap) has made the ringing more evident. By that I mean the after the tap the loudness of the hum increases and then oscillates till it returns back to a quieter steady hum.
Excuse my ignorance, but my thoughts were that tightening the screws could have improved transmission of vibrations to either a bad tube or a bad solder joint. I figured that conduction at a bad joint might temporarily improve with the vibration, but I couldn’t convince myself that a faulty tube might also show the similar behavior – perhaps a faulty connection in the tube or small changes in the plate/grid/cathode distances (i.e. one of those components vibrates).
I also hear popping sounds (not with headphones on) when the tubes heat up and cool down, so I would guess that something is changing shape during the warming/cooling process. I assume that this is not unusual.
If this is sounds reasonable, I will give the tubes additional burn in time. If nothing changes I will re-wet the 1, 2, 3 and 5 pins on the octal socket, terminals 1, 2, & 3; on the nine pin socket the center pin and pins 3, 6, 7 and 8; also clean the tube pins. Yes, I know it would be quicker to just re-wet everything, but a part me wants to try and narrow done where I might have goofed. Unfortunately, I do not have any other tubes to do the easy test. I’m also not sure when I will get some and the hum level is tolerable in most cases. I realize that right channel extends further back and forward than I am checking, but I kind of want to see if any changes occur first before extending the search.
I do want to sort things out and adapt to the sound before doing a speedball upgrade. So, unless there are any other thoughts to consider, I’ll report back in a week or two. Sorry for the long post.
