Replacing power tubes without re biasing?

[Hiwatt]

Hi guys,
I know this is not normally meant to be done but would I be able to replace my power tubes(2x 6L6,Matched pair)without biasing the amp without causing any damage?
I do not have the know how nor a multi meter to be able to do so.
It's a fender Blues DLX and it's beginning to sound a bit "thin" as it has the stock groove tubes which are at least a few years old and have had plenty use!
It's not been re biased since new so is biased from the Fender factory which I believe is a bit cold?
I've got a gig at the weekend and I would quite like to put the JJ 6L6's in it along with new pre amp tubes.
Any advice is much appreciated.

[phantomman]

A proper idle bias adjustment is imperative to optimize the output stage, both to extend the life of your power tubes and coax the best tone from them. If it's never been done, doing so now (with the original brace of Groove Tubes) might just surprise you in a very pleasant manner. Find a qualified tech and let him have a go at it.

[chuckocaster]

On such short notice you might as well just put them in there. Be sure to do so soon and play it for a bit to make sure everything is functioning fine.

But getting it biased will make sure you are getting the best tone and life out of your amp. Just like a car, if you neglect regular maintenance you can surely expect problems down the road.

Best of luck!