Left channel fading in and out

Thank you all for good advice.

Can anything be eliminated as a potential culprit? I was going to ask whether tubes could be crossed off the list, but just saw Bifwynne's post...I was also going to suggest the speaker since I'd think any damage would be fairly obvious, not as subtle.

I will recheck the cartridge alignment. I actually checked the VTF that very same night before I started hearing the problem, and it was as intended. I probably have about 1000 hrs on my Delos.

Bifwynne,
The speaker cables are the Anti-Cables (solid core copper with a thin layer of coating) with bare ends so switching L and R would most likely not show anything.

I checked the tubes and the bias was spot on. They are relatively knew as I replaced them in late July. I'm of course talking about the power tubes in the monoblocks. I don't know how to check the input tubes in the power amps and the tubes in the line stage. Those are over year and a half old.

I might contact Rogue Audio to get Mark's input on the tubes. In the meantime, I'll follow Al's advice, which is always a good idea :) Thanks again for the suggestions; I'm pretty bummed about this.

It appears it is the speaker, after all. When I turned the system on, with the volume knob all the way down, I heard some crackling sound coming from the left tweeter. When I turned it up, with no music on, the crackling disappeared, but the fade-in and -out continued with the music playing.

The night the problem started, I apparently put a record's sleeve on the volume remote by accident and left the room to get a drink from the kitchen. With a delay, the volume began to go up. I ran back to the room, and a friend of mine who was in the room, grabbed the remote and turned the volume down, but the knob must've have gone up almost all the way up for a second or two. It is possible that it caused some damage to the tweeter. I'm surprised since we listened to several records with no issues after the remote incident before the problem revealed itself. But at this point, it's seems to be pointing to the speaker. The SR-17.5 from Silverline Audio are incredibly well-made and I know they can handle a lot (apparently max output is 126 dB), but I guess all it takes is a moment of inattention and bad luck sometimes.

Al,
Yes, the low level hiss is what I would usually hear with my ear close to the tweeter. But when I powered up the system today, that hiss had some crackling as well.

I checked the cartridge alignment and it was correct. I will start the check as you suggested. If it's a tube, would it be one of the power tubes or the input/driver or line stage tubes?

I decided to switch the speakers to see whether the problem would remain in the left speaker or move to the right one. I figured this would allow me to at least eliminate the speaker as the source of the problem.

The fading in and out appears to have moved to the right channel, so I'm now pretty sure it is the speaker, not any of the tubes. Puzzling, the effect seemed less frequent after the switch, but it was undoubtedly the right channel that was fading in and out.

Al,

I did hear crackling for a few seconds, which I immediately attributed to the problem, but it has disappeared since and I did not hear it at all yesterday when I switched the speakers. I always hear low level hiss from the tweeters with the volume know turned all the way down; perhaps the crackling was the result of some irregularity in the current that manifested itself through the speaker. I'm not sure how else to explain it. However, it is puzzling that after the switch the frequency of the fade-out seemed to have decreased, even though it was still with the same speaker.

Doug,

Yes, I physically swapped the speakers so that the right monoblock was now feeding the speaker that used to be the left one (the one revealing the problem), and vice versa. I didn't touch the cables at the amp terminals. The fade-out appeared to have moved to the right channel with the speaker. I'm in the process of contacting the dealer I bought the speakers from to see what my options are. I think they definitely need to be at least checked out.