You have bad coupling caps in the phono stage. Providing the line level section is working fine that is most likely it. There is not much to the table, if it spins and the cartridge is new and mounted properly and is a high output such as your shure then you can assume the phono stage is the problem. The low level oscillation is usually caps. How good are you with a soldering iron? Also, go on the Dynaco Doctor website and they will help with the pre-amp. Don't give up; that is a nice set-up. The arm on the 145, the TP 65 is the weak spot but is serviceable until you can up-grade.