Tubes for H&K Fortress bass preamp?

[PreacherX]

Hey!
I just bought a Hughes & Kettner Fortress Bass preamp with Tube-distortion and DBX compressor. The preamp sounds amazing and the compressor does the trick perfectly unlike alot of other built-in and pedal-compressors i've tried. The only thing is that i'm not really happy with the tube part of it.
I play in a thrash/death metal band and a grindcore band and most of the bands i record are pretty heavy and usually want a little or alot of distortion on their bass tracks.
Putting in the tubedist sounds okay, it does deffinatley break it up a little bit but i wonder if i could get it to distort even more by putting in new and different tubes?

I opened it up yesterday and the tubes in there were original H&K CM1's so my guess is that they've never been changed and might be a little tired after all these years, so a switch might just be in place.

Could anybody point me in the right direction for getting (hopefully) alot more distortion, but still keep the fatness of the original bass sound as much as possible? Even if it just distorts a little more i'd be happy.

Oh and yeah the tubes are standard 12AX7/ECC83's.

Thanks in advance!

[Mikhail M]

Hey man!
I own the same preamp. Tube section is not tube distortion - it's tube channel of the pre. You can get some dirt there for shure but if you want more you'll be better of with some distortion pedal. You can place pedal before pre or in parralell loop - so you woun't loose low end.
Changing tubes will make you sound a lot cleaner(yes - you may loose some dirt!) depending on the state of CM-1 - mine where nearly dead.
Possibly you can use very "hot" 12ax7 but I am not sure if even that will add drive you want. Get a good pedal

[muziekschuur]

Nice OCD pedal in front of it?