Lots of radio manufacturers had radios available for 30's and 40's vehicles. Allstate Philco Motorola Firestone and some others could be had. I have one for my '45 GMC whick is 6 volt Pos grnd. It's a 2 piece unit. A head unit goes under the dash and the main tube chassis goes against the firewall. It's not installed yet, because I have more mechanical items to go before I'm ready. I bought it a while ago. I need to dig it out again and see what it is!
