I recall the C7A-Revised being a fantastic sounding preamplifier. If you have merely a C7A, perhaps investigating what exactly the "revised" referred to would be an excellent starting point. Perhaps some generous "revised" owner out there would be willing to take a few detailed internal photographs for you to examine, as well as answer a few questions about the circuit changes in the "revised" version.
Cap upgrades are a crap shoot at best. Often, a designer will use seemingly pedestrian parts that are perfectly voiced into the circuit. Changes will render differences, but only your ears will emphatically tell you whether boutique parts are actually better. In my experience, you have a 50/50 shot of actually improving things without destroying the fundamental characteristics of the unit; presumably, it's these original characteristics which made the unit both worth keeping for an extended period, and worth attempting to improve. You takes your chances.
-Richard
Cap upgrades are a crap shoot at best. Often, a designer will use seemingly pedestrian parts that are perfectly voiced into the circuit. Changes will render differences, but only your ears will emphatically tell you whether boutique parts are actually better. In my experience, you have a 50/50 shot of actually improving things without destroying the fundamental characteristics of the unit; presumably, it's these original characteristics which made the unit both worth keeping for an extended period, and worth attempting to improve. You takes your chances.
-Richard