Polarity on your transformer is not a problem since you have AC current on your secondarys find your primay and it's center tap the the secondarys and it's tap and your set to go, I have NOS transformers for that radio, DELCO's I bought out a UNITED MOTORS radio shop,SORRY they are not for sale, I've made a list of parts interchange parts of GM radios. That power transformer maybe alright, most likely it's been heated up by a bad buffer, give your transformer a chance they are a rugged unit
