About 2 weeks ago, an issue started with my system with the first symptom being a constant hiss in the right speaker.
After checking everything that could be checked (including cables, preamp, switching speakers, speaker rheostat (AR2AX) etc...), I noticed today that my ST70 tubes (all having very close values and being quite new) do not hold bias anymore on both channels: whenever I check the bias on each channel, values keep moving up and down quite rapidly. Yet, sound is great on the left speaker but the right speaker stills makes hiss and 'pops'.
My ST70 is a stock one, with only the PC-3 caps having been replaced with orange Sprague by the previous owner who also changed the output RCA connectors. Regarding the latter, touching them when plugged in the amp sometimes creates some kind of interferences in the right speaker as well.
Does the selenium rectifier have to be removed at first? What key areas should I pay attention to?
Should anyone have an idea of diagnosis or any area to be looked at would be welcome.
Thank you very much in advance.