I am the owner of a st70 in stock condition. Lovely unit.
It has some hum which is, however, not noticeable when the amp has warmed up. The hum has been there since i bought the amp last november.
Now, I suddenly the other day, noticed a lot of hum in the left speaker while the other speaker was quite.
As i turned on the music, the left channel (the one with the hum) passed only a weak signal through, while the right speaker output was normal.
I got a little scared and turned off the unit. The tubes should all be fine (they all glow and bias is stabile), Mullard GZ34 is new.
Does anybody now of this fault and has some experience what to do next?
The bias voltage is stabile in both channels at 1,5 V. The selenium rectifier, black cats and the quad caps have not been changed. Nor the big can at top, as i know off.
Thanks everybody in advance.
Bet regards, Johannes, Denmark