[R-390] Motorboating on R-390A

[R390rcvr at aol.com]

Good day all:

Nice weather here in Michigan, about 12" of snow, and soon to be 30 mph 
winds!

I just put a Motorola R-390A up on my bench for the first time. The first 
sympton that popped up was   motorboating on all bands.   It occurs every 70-75 
KC, like clockwork. In some cases, it is louder with the BFO on. It disappears 
with the antenna disconnected. The motorboating is 5-7KC wide, with a slight 
peak in strength centrally. I have subbed every tube except the rectifiers, 
3TF7 and OA2 without any effect. If there is a very strong signal, it isn't very 
noticeable, but in quieter areas of the band, its is quite loud. I haven't 
found any switch settings that effect it at all, except, not present in Calibrate 
setting.

I would appreciate any thoughts you might have.

Thanks. I will be out shoveling for a while!

Randy Stout