Threshold - S/300 Was there a Series 1 & Series 2

Hello -

I'm trying to narrow down on a Threshold amplifier.

Can anyone tell me if, in the "S" series,was there a Series-1 and Series-2?

I'm looking at an S-300 but don't know how to tell, or what the difference would be?

Any help would be appreciated!
I owned a S300/2 It was a series 2 ( non Optical Bias ) ...List$ was around $2300-$2800 depending on year made.......Great amp!
I think the Series II says so on the front badge. The early S/300's, both Series I and II, say "overall feedback free" on the front. These have light grey tops and rear aprons. The later models S/300 say "optical bias" on the front, say class A/AB, and have black tops and rear aprons.
I agree with Rockvirgo.