Spider Valve 112 possible bad tube

[pickerta1]

first time poster....i have a spider valve 112 and haven't really used it very often over the past few years.  it got some legit use for awhile but never heavy years back.  i have never replaced any parts on it or had it serviced....so it is obviously over due for new power amp tubes at the least.  Lately when i fire it up it has a lot of crackling (more than the normal amount when adjusting volume) but the main issue is the output seems to be fluctuating randomly and I can't seem to get a steady volume output.  I checked my cables and i am pretty sure the amp is the issue but it could possibly be my electric guitar since i dont have a second guitar to test at the moment.  any ideas what this sounds like?  Happy to share more detail if helpful.  I bought some Sovtek 5881WXT matched set power tubes in preparation for having to change them out as i assumed that would be needed soon regardless.  I would love to think I can swap them out without endangering myself or my amp but there really are not enough instructions in the manual to do it (they obviously want you to take it to a pro).  I may go that rought but would love to know how i can safely swap them out and see if that fixes it without doing the biasing?

 

thanks!!!

[psarkissian]

Judging by the serial number, lack of a service history and crackling,... I would say yes, it needs a full set of tubes,

including the 12AX7 China B pre-amp tubes. Sovtek 5881WXT matched set are the correct power tubes, very good.

 

There are no instructions for doing this yourself, because the shock hazard is too great. One accidental slip and you get zapped.

Been dealing with tubes 55+ years,... I still get zapped every now and then. It hurts.

 

Leave it to a Line 6 authorized service center in your area, who can do the tube replacement and tube bias.