No idea how to fix it. Why not state where you are located in your sig. On this forum you have every chance that someone lives near to you and may be willing to help. At this short notice I would borrow (buy cheaply) another amp for the gig. Can you go through the pa system? if so use some form of DI box? - plenty of pedals etc about that will do this cheaply e.g. https://www.gear4music.com/Guitar-and-Bass/Behringer-BDI21-V-Tone-Bass-Preamp/6LV?origin=product-ads&gclid=CjwKCAiAxMLvBRBNEiwAKhr-nGbKu9STsEB9lf49014ynlw8pt8J4MrQ_kPzBsJNkDy3dicY3LBFxxoCXr0QAvD_BwE
I always carry a Sansamp as a backup for the 'failsafe' scenario. Good luck with the gig.
I managed to get the truss rod to lift and snap the fingerboard on my G&L 5er (older single action rod, not an uncommon problem apparently). Repaired by Jon with a dual action rod, better quality fingerboard, outstandingly good stainless frets and an almost unnoticeable repair. Outstanding workmanship (better than it left the USA with) and the bill was unbelievably low.
And another pedal (tuner) despatched from the Travis trove. Excellent communication, packaged to survive and rapid arrival. The B string on my 5er can now be tuned. Many thanks.
Basses and bass kit fall into the exceptional need category. This category of purchases is deemed essential to life function, happiness, stardom, sexual prowess, fame, playing ability, tone (underline all applicable)..
Aria spirit PE bass, bought on this very forum. No pics at the moment but google "Aria spirit PE bass" and it is the blue one. Seriously well built, nice and light, superb balance - no neck dive, active electronics. With a 32" scale length it should be a 'killer' but lacks 'bite and aggression' compared to my other basses.
I have two (go figure..) Peavey Tour 700s. Indestructible, not too heavy, not Class D and reliable. (500W into 8 Ohms is useful) Tone is good for what I want, I can get some 'valvey' grit / distortion (think Andy Fraser on the Free Live cd). Graphic is good, the cosmos is a waste of time for me. Where are you based?
The 301 is imo one of the best looking bass cabs ever. Just need a 2019 301 lite, looks like a miniature 301, has modern lightweight internals and construction. I see a project