arpsum wrote:But who designs such amps for both instruments in a same cabinet?
Arpsum, you must be a youngster.
In the 50's and 60's, Leo Fender specialized in building versatile amps. In the old days it was common to plug more than one guitar into a single amp. For more than five years our bass player plugged his Mosrite bass into my '65 Fender Bandmaster piggy back while I played lead. He didn't even own an amp. Back in those day's it was common practice, especially since we couldn't afford two amps. The Fender Bassman is a prime example of a versatile amp. It was designed as a Bass amp but readily become most popular with guitar players. However, I think the Ventures could afford what ever they wanted. It was probably just more convenient to use one amp.