Great sounding early Mac SS pre amps? Have you already exhausted all the easy searches like finding the Loch Ness monster and Bigfoot? The tube units may be collectable but from my long ago experience with a C8 that does not mean they sounded good. The circuit was far too complex. The 7C was the best early stereo preamp closely followed [or proceeded, according to some] by the PAS 3 Dynaco. For sound quality you would get far more for your money with a more recent unit from a good company. It would also not be nearly as likely to need repair or updating. If quality early SS is a must Accuphase or Lux made pre amps that were very well built and sounded better.