Left channel fading in and out

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?

If it's a tube, would it be one of the power tubes or the input/driver or line stage tubes?

Don't know; could be any of the above, or something else. The fact that crackling occurred with the volume control all the way down, though, most likely indicates that the problem is either in the amplifier, or in preamp circuitry that is downstream of the volume control (for example, the output stage of the preamp).

Best,
-- Al

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.

Marek, nonetheless I still find it hard to conceive of how a fault in the speaker could result in crackling from the tweeter when the volume control is turned all the way down. The likely cause of that kind of symptom would be a problem in either the amplifier, or in preamplifier circuitry that is "after" the volume control. Perhaps:

(a)The crackling and the fading are being caused by two different things. Or,

(b)The problem is being caused by the amplifier or preamplifier, but there is an intermittency involved which causes it to appear in different channels at different times. Or,

(c)Slight differences between the impedances of the two speakers result in an amplifier problem being triggered by only one of the speakers.

Best,
-- Al

Actusreus,

You said you "switched the speakers". Did you literally move the L and R speakers across the room or did you swap L and R speaker cables at the amp outputs? Makes a big difference in the interpretation of your results.