I actually play guitar but have recently been using a bass rig alongside my guitar amp for an octave-down clean bass signal (in a two piece rock band). I have just bought a really old Fender Bassman 115 cab, and all the cab tells me is that it is 8 ohms and has a 15" speaker. I can't open it up because there are no screws in the cab, it's all permanently closed up the way it's built. I'm currently running an old 80's Hartke 1400 head through it which is 140 watts and 4 ohms (don't think this is ideal, 4 ohms into an 8 ohm cab?) that's the way I bought the rig second hand.

I'm thinking of upgrading the head to something cheap but louder like an Ashdown MAG300H EVO III, which is a 307 watt head unit (which says it runs at 4 ohms "minimum")... would this head work with my cab? Does the ohmage need to match up? I always thought (from using guitar amps) the ohms had to match, otherwise something will break.

Also, does anyone know how many watts a typical old Fender 115 cab would be? I read somewhere the new ones are 300 or 700 watts.

EDIT: Just found out the cab is 150 watts as it's an old model... now looking at an Ampeg Micro VR head instead
Last edited by loop-de-luke at Nov 17, 2013,
The ohms don't have to match, but the impedence of the combined cabinets should be equal or higher than the rating of the amp. With a 4ohm amp, a 4ohm speaker would be fine, as would an 8 ohm speaker, or 2 8ohm speakers, 1-4 16ohm speakers and so on and so forth.

I've owned the MAG300. It's rated at 307w into 4 ohms, so to get the full draw, you would need a 4 ohm cab, or two 8 ohm cabs (the head has two speaker outputs). You'll get around 180w from the MAG into your Fender cab.
Last edited by Deliriumbassist at Nov 16, 2013,
I emailed Fender about the cab, apparently it's only 150 watts because it's an old one, the new ones are 350 watts!! So there goes that idea about the MAG300...

Looking into an Ampeg Micro VR 200 watt head now, as that's 4 ohms so should run at around 130 watts with the 8 ohm bassman cab... is that a good idea or is it too close to the cab's max handling? Also, would that even be loud enough for big gigs? It's to stand up against my Marshall Plexi stack.... although the Ampeg does also have a DI