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The stock amplifier in the "classic" tube Leslies produces 40 Watts. It's a great amp and has a terrific sound but it has a tough time competing on stage with a guitar amplifier at full honk. It's not surprising that a common modification consists of some method of achieving higher power. This usually involves replacing the amplifier or else powering the Leslie from an external amplifier. The increase in power will probably require a change in drivers as well. (You probably did that anyway when you blew up the treble driver).
One modification to the 145/147 amp you might consider is to add grid resistors to the output tubes. As stock, when the amp is overdriven heavily, the output tubes can start to draw grid current, which can produce some harsh-sounding clipping. You might add a 1K-5K ohm resistor between (the intersection of the .1uf cap, the 100pf cap, and the 220k cap) and the grid of the output tube to smooth out the clipping and provide a more gradual onset of distortion as the amp is overdriven.
Also see LeslieDriverReplacement.
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