Well any vintage fender tube amp is pretty much the identical preamp to what Alemebic sold as their high end bass tube preamp back in the day (it was just a copy of the standard fender preamp section). So a twin reverb with the built in speakers disconnected and a bass cabinet connected should sound just like a Fender 100-125 watt tube bass amp. The particular amp I'm using is too bizarre though and not one you'd normally find for sale - it was an accordion amp from the 50's made by a company called "Sano" and is full of Amperex tubes. My brother in law bought it new in the 50's and it cost him a fortune back then. It's not worth much on the used market but I could sell the virtually unused Amperex tubes for much more than I could get for the complete amp.