Yes, that is true. It takes a lot of heat. By the way, I have gotten the schematics and service manual (a minor one) for the 223 and 226. From what I understand it is the same radio, but the 223 was used in the Dart, and the 226 was used in the Coronet. Bendix 56ML. Then today I have been driving around the city to find a 12 volt battery I could use as a power supply for the radio. So, the day was at an end when I got back home. Hope to look at it tomorrow.
Bill