Hi everyone, hope you're keeping well

Just ordered a new set of tubes for my 6505 head... the dude that's going to give me a hand for the re-tubing asked me whether the head needs adjusting bias or not... after pretending I understood fuck all, I thought I may as well just ask here, if you please gents. Thanks in advance

Kindest regards 
jonalcover From what I see, it is fixed, ajdustable bias which means the bias is fixed by a trimpot, which is adjusted by the user/factory. BUT, the amp is set from the factory to be very cold so that it works with a wide range of tubes without needing bias adjustment, and also having it so cold keeps the amp from being too "spongy".

If your tech knows what he is doing, he could adjust the bias so that the tubes are working optimally. Or he could just leave it alone and just "plug and play".
If it's truly a 6505 and not a 6505+ head, then you can't bias it at all without the bias mod.  The 6505+ can be biased internally.  But, they are both designed to run optimally with a cold bias and are set that way from the factory.  You can just buy a matched quad, put them in, and fire away.  However, some people swear they sound better when biased hotter.  Others prefer them cold.  Honestly, I think a warmer bias only helps at low volumes, as that is where crossover distortion is most prevalent.  With fresh tubes, both of my 6505s sound pretty beastly, so I haven't really been concerned about changing the stock bias setting.

I did have a set of JJ 6L6s once though that had a bias point rating of "22" on the boxes from Tube Depot.  All of the others I've had were rated at "20."  That set that was rated at 22; I swear, sounded marginally better.  But that could have been a coincidence or just better sounding tubes for some other reason.