Early HK Citation amps and preamps used very wide BW designs, and they learned to capture RF and before it reaches the amplifier stages, while retaining the wide BW design that had trickle down improvements in the audio range.
The idea that RF is rmoved at the power regenerator isn’t ideally true. There are plenty of antenna after that regenerator BOX where RF can get in. The noise is a serial circuit box problem and it isn’t just the AC. You want to design a low impedance RF path to ground nearest the amps input stage that you can to remove the chain of residual interference.
Some devices need RF traps at the ground on every circuit block to not overload the next block or that specific block, it all depends on the gain BW product at high frequencies.
Wide BW amps sound good, and will of course amplify RF that we don’t want. We made the amp able to amplify RF and then we deny them the RF signal to amplify while retaining the advantages these amps provide in the analog spectrum. Wide BW amps are always willing to strut their high BW stuff given the chance. The ability never goes away, just the presence or abscence of what’s in the input signal.
Best,
Galen