There was something on this over at tech talk. Post it there and you will get a quick answer.

Check this article on fletcher's site. I believe he describes the difference between silver and black face.

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The black face uses low noise fet's and the "silver" discrete transistors. Both are desireable pieces.

The retifiers are different in the PS.

Bob O. can get more detailed as per sound. I never had them side by side for comparison..just one vintage at a time.

Just curious why a purple audio over the real thing? Wouldn't the original have the added advantage of a better resale value?