I'm only new to playing guitar and I want a new head, I've currently got a Line6 Spider IV 150w Head and a Line6 Spider IV 4x12 Cab. I'm looking at the Peavey 6505+ or 6505 head but I am wondering if I would be able to plug it into my cab without any problems. Should I get a new cab with the head or will this one be fine?. Any response will be greatly appreciated, thanks .
It'll be compatible no problem, but I've heard and seen on a couple occasions that the stock speakers are quick to blow out in the spider iv cabs. that's not to say it's going to happen, but I'd consider upgrading to a better cab at some point in the future to better suit something nice like a 6505. Either way, as long as the cab works, it works.
Compatible with a 6505? Most likely.

Work until you get something better? Sure.

Sound really good for the long term? Probably not.

Unless you have a Spider VALVE cabinet then you are good to go.

Celestion V30s go a long way with 6505 family heads.
Ibanez RG1570 Prestige
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .