@goofyfoot , the sources of pitch variation are a bad motor control unit, warped records, slipping motor pulley and bad belts. First and relatively cheap is replace the belt, clean the rim of the drive platter with acetone or brake cleaning fluid and make sure the motor's pulley is tight. Also clean the motor pulley. Do not get finger oils on the belt. Use gloves when you handle it.
Meandering Pitch, Where’s The Problem?
As I’ve mentioned in other posts, I’ve been modifying a Thorens TD 160 MK1. It is and will remain a dedicated mono table. Currently, I’m using the original TP 16 MK1 tonearm with an AT 33 mono cartridge. I will eventually replace the TP 16 with an Origin Live tonearm and EMT mono cartridge. I still however like playing records while in it’s current state. What I’ve experienced with a number of classical records is pitch instability. Primarily when playing piano recordings. There are certain passages that are a problem and I’m not exactly sure the cause. My cartridge is aligned using Baerwald. I understand that with some records, especially very old mono vinyl, that the pressings could be off but if that were the case, then the entire album would be an issue. I do need a new belt but I’ve still had this issue with a brand new Thorens or Origin Live belt. Just wondering what others think and if there’s an antidote? Thanks!