Audio Space Ref 3.1 KT88 - biasing

I've just got hold of a Ref3.1 Kt88. Great amp, but want to change the KT88's. Haven't got a manual and can't find anything online about the correct bias setting on the VU meter.

The stock tubes are set at '9' on the scale. So my question is: does anybody know the correct setting and what make the 'stock' tubes are?

I have put a request into Audio Space, but no reply yet and as these amps aren't available in Australia, there's no service advisor.

Thanks in advance.
It is very easy. Bias all tubes to the "0" on the bias meter on the front of the amp. Don't forget to turn the bias screws to the left to lower bias before you start for new tubes. If you have any further questions, email me. I have had my AS for just over two years. Upgraded tubes make a huge difference in this amp. Good luck.

Thanks for the response - it's great to get this online help! So are you saying that "0" is the correct setting? That seems to make sense, but it's a long way from where mine were set.
What tubes have you used? I'm thinking of Gold Lion, having run these in my Quad amps. I've already changed the 6SN7's to some vintage RCA's.
It's a heavy amp isn't it. Had to make a trip to the physio to get the back tweaked after setting it up!!
Yep. My manual says...turn the meter range to v1 position. With a small flat head screwdriver, adjust the bias voltage for v1 by turning the bias pot (v1) located on top of the chassis. Adjust the bias pot until the indicator of the analog meter on the front panel is pointing at the 50mA mark on the bottom scale. Repeat for the three other tubes and you are done! My stock AS tubes drifted bias quite a bit. My Gold Lion KT88's are rock solid. I'm using Sylvania NOS 6SN7's and vintage Telefunken's in the phono. Hope this helps.