These were my demo M-1s until I recently upgraded to A-1PXs. The panels were rebuilt in 2009 and have the latest PX stator wire insulation and PX membrane. They do not have the PX stator lattice structure and they are 90 degree horizontal dispersion (standard PX dispersion is 45 degrees). The backplates have the toroidal transformers/high impedance upgrade and the solid state bias supplies. They are in very good cosmetic shape and in perfect operating condition. For those not familiar with Sound Lab full-range electrostats they are probably without equal in terms of clear, non-fatiguing sound with incredibly accurate timbre (tone color). I am an authorized Sound Lab dealer.