Further discussion with my friend today about the frams involved a feeling from him that late production 604c's had frams that were special by accident. Something about the metallurgy and they way the material from the supplier came through.. He also said they have a different part no. I have not cracked open the drivers to confirm. These are untouched so I don't plan on doing it. This afternoon, I had some time to play and picked out a few albums that had excellent bell ringing sections.. doing an A/B test in mono with the speakers being switched back and forth from amps. There IS a slight difference. The one speaker he stated as having the stellar fram does have more sparkle. I bought this pair of speakers from the family of the original owner. He purchased them NEW as a pair in late '57 for his audio service/sales shop. This was a backup pair in case anything happened to his main pair (four purchased at the same time).. These speakers saw very little use. They are pristine and untouched both with 1957 stamped on the basket. I am using a Fisher 400c and a pair of Heathkit W4's that I rebuilt as twins and have hotrodded and upgraded to use 6L6GC's.. a matched quad of new tubes from Tube Amp Doctor. So for all intents and purposes we have matching amps. All listening tests were done in mono.. so without question the one 604c has more sparkle (super stellar).. the one that doesn't still sounds stellar! But there is a minute difference. Anyway, I'm not trying to be nit picky, I absolutely love the sound of both speakers.. I was just hoping someone could confirm these findings or expound on it more. I love the history behind these things and if there is information out there it's great to keep it alive. Thanks, Pat