Have had this problem before, with MIT SC and classe amp, would send the amp into oscillation, never figured out, MIT checked the cable and was stumped, the cable and amp would not match up. That was the solve, no other cable caused the problem.
Make sure your rca's to your amp if single ended....are installed properly, ie, tightened so the ground is making good contact. Had this problem with WBT's once and it always happened when the system had been playing and heated up. Pliers fixed that problem, a barrel on one cable was a little too big for the inputs.
Did you find out if your tube preamp was passing DC? Could also be a loose solder joint around the tube socket from swapping out tubes.....have had that happen also.
Double check cartridge clips and wire/solder connection to the clips - has not broken or been compromised....have had that happen also and ended up sending my phono pre back only to find out it was fine....
Stay in this hobby long enough and just about everything will happen eventually....you will find it, good luck!
Make sure your rca's to your amp if single ended....are installed properly, ie, tightened so the ground is making good contact. Had this problem with WBT's once and it always happened when the system had been playing and heated up. Pliers fixed that problem, a barrel on one cable was a little too big for the inputs.
Did you find out if your tube preamp was passing DC? Could also be a loose solder joint around the tube socket from swapping out tubes.....have had that happen also.
Double check cartridge clips and wire/solder connection to the clips - has not broken or been compromised....have had that happen also and ended up sending my phono pre back only to find out it was fine....
Stay in this hobby long enough and just about everything will happen eventually....you will find it, good luck!