Frank used to be a Hiwatt guy. I think Tommy used Marshalls. I saw them in the mid 90's just before Tommy left the first time and they had a ton of vintage gear on stage. Last 3 times I've seen them Frank was playing a JCM900 and Dave was playing the Jubilee Slash head. Frank had a signature head with Modern Vintage amps that was based on a Hiwatt. It never really took off and I think after that is when the 900's came along.
I've seen them the last 4 tours. They have used Blackstar's on every tour. The live sound is incredible. I did notice that Frank really likes to use a roto vibe a lot, which you can hear on Love Song and on a lot of other tracks once you know that it's there. There is a youtube video of him showing his gear.