#1
I have a solid state 200 watt head that I bought with a 4x12 cabinet with it, they were not the same brand and were used. If I buy a vox ac tube amp which is 4 watts, will that work with the cabniet I have?
tpt
#2
As long as you make sure the ohmage is matched up,
yes.
A low wattage head can drive higher wattage speaker cabs fine but its not recommended to go the other way around
#3
The cab you use with the Vox AC4 needs to be 16ohms.
Gear:

Guitars
PRS Santana SE
Ibanez MBM2 EMGs
Fender MIM Roadhouse Strat
Ibanez AS93 BLS

Amp
Carvin V3m
Blackheart 4x12 cab

Pedals
Electro-Harmonix Metal Muff
Zakk Wylde Wah
JamMan looper delay