Hey there, buddy
You're tubes were "broken in" after about 10 hours (if that is even necessary). The only thing that may change with a tube is to burn off a bit of trace contaminant gas that may have been introduced. And that takes next to no time at all, certainly not 150 hours. The other thing is to let the tube warm up before use for a few minutes before listening for optimum operation of the tube.
What you need to remember is the bias of the unit in relation the the tube swapping you are doing. If the bias is off, you may be shocked at the difference in sound from correct bias to what it may be now. Problem is there is no bias adjustment on the unit as far as I know.
GE is quite old, as you said could be bias related.
All other tubes new.
I wish you are right.
Well, my experience was different.
At the beginning, the rectifier sounded dull.
After several hours, it got better and we like the sound when it was paired with JJ.
After 40+ hours, there is a some loss in bass and followed by increase brightness. Example, cymbals was definitely sound way off right up front. Male or female voices was sharp, lot of 's'. My left ear was irritated after long listening.
I started switching signalling tubes. JJ to EH to 6H6.
Followed by setting dsp equalizer and dropped 7kHz onward down a fair bit.
At the moment, dsp equalizer was removed.
Some brightness, at least not all music. My ear no longer feel irritated.
Hopefully, Sophia gets better, else another hunt for rectifier.
Or as a friend said, get a subwoofer.
