Blktiger0

If you're using stock Marshall 1960 cabs, they'll have T75's. If you're sure that they're V30-loaded, then that can be ruled out. If they're T-75's, though, that could be the issue. A scooped speaker with a scooped pickup would probably cause issues. In that case, since you'll be using something different live, you could either just risk it, throw an EQ in front of the amp, or swap them out for something more mid-heavy.

Personally, I don't see why you're using different gear for gigs than for band practice. That's just gonna reek of issues when you go to play live. It's no likely you'll have time to sit on stage and dial in a good tone, it'll pretty much be run-and-gun. It could be different for wherever you're playing, I suppose, considering I've never had a venue provide gear to play through, either. For me, band practice is where I perfect my Live tone. You'll never have a tight sound live if you're always using different gear. With consistency, you can do little tweaks over time that gradually make your mix tighter and tighter. You can personalize tubes, speakers, etc. when you're using your own amp that is consistent throughout gigs an practice, not to mention make EQ tweaks that you notice over time to really give your band a great mix. Obviously, the sound man, acoustics of the venue, etc. all play a role, but if you have your mix down to a science other than those factors, you'll have a happy sound guy and a more consistently tight mix. Just something to consider.

Also, sorry, I tend to ramble on...

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My Rig:
Moser Bastard V
- Pups: Bridge
Epi Les Paul Standard
- Pups: Bridge Neck
Egnater Vengeance
- JCA24S w/WGS Retro 30s
- ZW-45 Crybaby
- MXR 10-Band EQ
- ISP Decimator
(^Those are links^ )