When I picked up my ST-70, it had 3 original Mullard tubes and one RCA replacement, and one of the tubes had glowing plates... I figured a set of new tubes was in order. Based on my budget and reading a few quick reviews, I settled on the JJ E34L's and went for it.
I plugged them in and biased them around the same as before (1.4ish due to what I've been reading about it not sounding any different and increasing tube life). Since then I've been a little disappointed in their performance; they weren't sounding as smooth or detailed as I remember even the old mixed set of tubes did. A little washed out, even grainy at times.
So I took the amp out of commission for a day, replaced the bias electrolytic caps, replaced the selenium rectifier diode with a modern one, replaced the speaker terminals with some nice gold banana plugs, replaced the aging power cord... the simple stuff.
When I plugged it back in and powered up, everything worked beautifully and the bias seemed to be more stable than before. I set it up at 1.4v again, but the sound was still thin and disappointing.
I did some reading and some suggest that the JJ E34L's should run with more current than standard EL34's... so I figured I should at least run them at the standard 1.56v. I moved it up to the high side of 1.56v and let them loose.
Man do they sing now! Full, detailed, and solid midrange. At least as good as I remember the amp sounding initially, if not better.
So, my questions: first, anyone else have similar experiences or recommendations on the E34L's? How far can I push the bias voltage/tube current without worrying about damaging the tubes or other components (power transformer I assume would be the concern). What is the risk associated with more tube current? Should I just go with what sounds best, within reason?
Thanks in advance, I'm just learning the circuit so any advice or tips are much appreciated.