Damned good question, they are labelled up with Valve Art labels and 30mA ia written on, so unless that was done at the factory (!), they have been biased by someone at some time. I'm really happy, it's so easy to listen to. The 'special' mains cable is sitting in my hall, unused.
Mega thread revival. After Chris kindly loaned me some 5670 valves (which I held on to for a little too long - sorry Chris), he inspired me to carry out a little tube rolling. I purchased 4 X JJ KT77 to replace my EL34, and after a bit of back off action and a little biasing drama* they are in and singing. Result: I think the KT77 give much better bass and treble extension, and the mids are not shabby at all. Very happy, thank you Chris!
* The issue I had was with the bias pots being reversed on the PCB for either pair of valves. I just couldn't get the one set to 37.5ma no matter how hard I tried, nowhere near. It wasn't until I adjusted the pot that was supposed to adjust the other valve that it all started to fall into place.
I fell out of love with the whole thing for a while - external pressures really. It sits there though and deserves to be played and I like to tinker so tube rolling was the obvious step. Not an amazing amount has changed but I'm back into listening now.