6l6 vs el34 in bandmaster clone

Hi guy's I have a jansen bassman, its a fender bandmaster clone. normally runs old rca 6l6's, but these hav died a hidious death:D. and i had some Siemans EL34's sitting there. so did the mods and stuck em in.

yip I am getting to the question

my guitar has single / humbucker coil switching, the amp used to sound ok with singles and fantastic on humbuckers. now with the El34's sounds almost the same as the humbukers DID on single coil but changer over to the buckers and its all trebel and ringey (icepick ?)

my question is
does anyone hav experiance with this type of amp and the 34's, is it the amp or the way old tubes, will new el34's be sumwhat the same or do i just buy another pair of jj 6l6gc's