I use a Marshall JCM 2000 DSL Head as my main bass head and a Fender Dual Showman as my backup. I wrote Marshall years ago to make sure there was no issue, the letter I have directly from them states to use a bass cabinet to avoid blowing speakers, but there are no issues with using a tube guitar head for bass. I also have had no problems running either amp at gig volume, and have never had to pin the knobs.
