I am lucky, I have a new ST35 & a rebuilt SCA35 (as power amp only). Both I have put in the ST35-BCU bias upgrade kit to & have done 3 additional critical changes. The Bias kit was constructed per instructions & I added the optional ground wire from the board for both amps. C1 was removed from both amps.
ST35. I also added 22uF cap & a 1uF auricap after 50 ohm resistor. Replaced C4 & C5 with .47uF caps (5x original value, biggest I could fit in).
SCA35. The power supply on this was already way over done, all sections are bypassed with 1uf auricaps & it is split into channel A & B right after the diodes. I replaced C4 & C5 with 1uF auricaps.
Biasing, followed all setup instructions. I then turned on the amp & let set for 10 minutes. Set bias per instructions. Both amps were dead stable still a week later.
Sound after the above work done EXCELLENT! This is a term I seldom use. The amps were ok, but I have been around long enough & heard so many systems to know what was lacking. The high treble is now perfect in its delicacy. The deepest bass exists now with all the air. I found the sound staging much more focused & wider. The sound was all around clearer more enjoyable. What’s so interesting is just a few changes made a dramatic improvement in sound. I would highly suggest these mods to anyone owning ether amp.
Go away, have fun!