These are about the simplest, no-nonsense distribution amplifers on the market. Made exclusively for BSW I believe.
A simple +/- 15V supply with two-three tab regulators and 34- NE5534’s. Yes, 34 of them.
This one needed a -15V regulator. That’s it. Simple troubleshooting- the light was out! Sometimes a $1.50 fix is nice.