[Texasrocker]

Hello Richard, motorboating is usually a bypass cap to ground issue, however there are exceptions. I took a quick look at the Riders schematic for the 37-89 over at nostalgiaair. I will make these suggestions. Go carefully back over your schematic and make sure a cap isn't missing somewhere. Check for good solder joints everywhere, especially to ground. I have run across several previously-hacked radios in the past where parts were missing and not replaced. Make sure grid #2 on both 6K7 tubes have appropriate condensers to chassis ground according to schematic. Also check the cap(s) to ground in the avc line. Make sure the choke ( twisted pair wire) part #11 on Riders schematic hasn't been accidentally moved during the recap. Also, make sure both 6K7 and the 6Q7 tubes have their shields on them. I have also had luck eliminating motorboating in the past by adding a capacitor or two out to ground in the appropriate suspect areas. To do this, take a .05/ 600v cap, use a jumper with alligator clips on both ends and connect one end of cap to ground. Use the wire off the other end of cap and touch it to suspect areas that need bypass with set powered on. Just remember to discharge the cap to ground between test points and work with only one hand near the chassis. Im sure others here can offer other suggestions as well.Best of luck with your restoration!