6BQ5/EL84 tube life

[goraman]

I have a Manley Labs Stingray with 8 TAD STR EL84 tubes I keep biased at DC .24 to .25 they used to bias up to .30+ though I never ran them that hot.
I have one that won't go passed .24 any more and the rest will just hit .26 to .27.
They have been in the amp since the two months after I bought it in 2007.
Are they near the end of life? or can I just open up the master bias a little to get more bias adjustment?
As there is a master bias pot in the bottom of the amp,because not all brands of output tubes will be in the fine tune range on top of the amp.
I'd like to get one more year out of them but if they dip below .24 good bye old tubes.
Would I be risking a tube failure and possible amp damage?

[goraman]

Duh,
I let the amp get up to temp and suddenly they all biased like new tubes.
Easily into .36 if I wanted .24 to .25 no problem.
I guess letting the amp get hot is critical to checking and setting bias.
I used to check every month when I first got it but since after a couple of years of nothing changing I got lazy and hadn't checked in a year and forgot they had to be hot.
Stupid is as stupid dose.

[realysm42]

Does ;)

[goraman]

Does ;)

My point exactly...:lol:

[realysm42]

I'm not sure if I fell for a pun or not now.

There should be a grab coat smiley in the advanced reply section :doh:

[goraman]

I'm not sure if I fell for a pun or not now.

There should be a grab coat smiley in the advanced reply section :doh:

Enter my threads at your own risk!

[DSJR]

Gently run EL84's should last decades if not run 24/7, shouldn't they? croft series 5's are only now returning for a service and many of these are twenty or more years old by now...

[Ali Tait]

If they still sound good, you're not getting hum, and no red plates, they're probably fine.