Over the last few weeks, the SQ from my 009 / BHSE had changed ( less dynamic ) so I decided to change the quad of PH tubes I was using, and put in the second quad I'd got.
And the SQ sounds to be back to how it was when I first started using the first quad, so it sounded like that first quad were ready for packing up.
I'd been using that first quad for over a year, but I haven't been using my BHSE everyday, in fact there were times I only listened to it 2 or 3 times aweek.
So if I'd been using the BHSE more often, then those PH's might've not lasted as long.
While I'm happy with the SQ from my 009 / BHSE using the PH's, for what those tubes cost I'd have expected them to last a lot longer.
So, I've decided that once this second quad packs up, I won't bother getting anymore, I will however try and get hold of a quad of the Mullard or Holland XF4DD's I'm reading good things about.
You could have the old quad of tubes tested to see if they are still performing at their original spec.