I use a dual 5150 slam in stereo. You can link them together as a master and a slave and use the master as master volume for both amps and cabs without any modification. I can't do this with my my Vox's or Marshall JCM
800s - only my 5150's. Here's my secret:
1. Junk the chinese tubes first and foremost. They are tone killers! If you have the cash and want the ultimate tone, find some 6L6GC RCA gray or black plates and some NOS Telefunken smooth plate 12AX7's.
2. I plug my guitar in to one of the 5150 inputs. This amp is the master.
3. I use the Preamp Out and run that into my Rockman Smart Gate/Rockman EQ/Rockman Eq/Stereo Chorus/Stereo Echo. One right output of my Stereo Echo goes in to the "Return" on the back of the Master 5150.
4. I run a cable from the left output of my Stereo Echo and run that into the "Send Return" on the Slave 5150. I run a 12 gauge speaker cable from the Speaker Out on each into into its corresponding cab.
That's it. The master volume on your Master 5150 will turn the volume up on both amps - I'll be damned how it works, but it does; could be since its an all analog rig (rockman gear and the tube heads). I don't use digital, so I don't know if a digital pedal will work or not, but I've been gigging with this setup for 5 years now.
Please email me with questions...