Overhaul SOLOS II, what should I replace?

[quickbird]

This is a solid state system that was built in 1975.
What, if anything, should I replace to be at optimal performance?

[HRobert]

I don't believe that the Solos II was manufactured in 1975...it must be a 1974 or older.

Rob

[noel]

Replace all the electrolytic caps.  90% of those will be in the power supply anyway but there's a handful throughout the rest of the amp.  From there look for obvious component failures (burn marks etc.).  To be really thorough cruise through the amp with a meter and a schematic.  If something is out of spec. change it. 

These steps would really be the same for any amp.  Pretty easy stuff, just make sure that its to print and check some voltages, you should be set.

[quickbird]

I assume that the electrolytics age poorly even just sitting on a shelf?
I have found some old stock ones but the date codes are early 80's.

It sounds very clean and is louder than heck. 
The tremolo circuit is not working.  I replaced all the BC107B transistors on the effects board since a couple were testing below spec and thought one might be the culprit.  It was not the only thing holding it back.  the little light in the LDR lights up but it is not getting "rate" signal.

Rob, you are right.  the test label is 2-13-74

[Isaac]

Yes, electrolytics age poorly on the shelf. In fact, they age best when in use. Counter-intuitive, I know, but that's my understanding.