Jadis Defy7
The Jadis amp uses two 12 volt filament windings using the 6 volt KT88 tube filaments in series.Very doubtful the filament windings will tolerate the increased current for long term reliability.Those amps are well known for reliability issues because Jadis uses 12AX7's in parallel to drive the outputs.They use 470K ohm resisters to load the input G1 grid,the tube manual lists the max load for that input grid as 50K,this leads to problems with bias stability and red plating caused by current flowing in the G1 input circuit.Jadis tests their tubes to insure they have properly aligned grids at least when new,after a few hours that can and often does change.This fault in the design is well known and information on it can be found with a web search.I have repaired a good many of these amps and owned several as well,the only tube I would use in the outputs are KT77s as they will tolerate the 470K G1 load.Cheers and good luck.