cleaned thoroughly (cable is a bit stained)
pre 1964 early version sr 1 with a lower bias voltage of 150v (later post 1964 version sr 1 was 200v) and a metal mesh on the inner baffle (later post 1964 sr 1 had a white plastic inner baffle similar to the sr 2/sr 3/new sr 3)
comes up immediately and no discernible channel imbalance (to me at least)
sounds very mid centric lots of rolloff in the lows and highs (if you looking for a better sound of this era stax sound go with a sr 3 or later which have a bit more extension on both ends and sounds nice and natural) though it seems to take bass and treble equalization well enough
do note that with the bias voltage at 150v you have to be a bit careful running these off 230v normal bias amps and not drive them too hard whereas the later sr 1 and beyond were 200v and can be plugged into a 230v normal bias socket (very tough to find 150v normal bias adapters/driver units like the srd 1 or srd 2 or sra 4s or sra 6s)
tested with a widely available srd 6 adapter (not included) which does drive the sr 1 if you are looking for something easily available (please note the srd 6 was bundled with later phones which were 200v bias so you may hear a slight hum when nothing is playing though it was not present when playing anything)
does not come with pads since original sr 1 pads all disintegrate (i am still trying out different replacement pads for the early sr 1 which has a smaller chassis and if i get a set that works well before the listing ends i will include them)
video of them working earlier this year: https://www.youtube.com/watch?v=m5xdXnYas3g
thank you!