Hartke Model 3500 MOSFET power supply

[Axtman]

One thing about this amp that has me puzzled is that the low voltage rails to the IC chips are +/-18 volts. That is the top operating voltage of the IC chips! That's like driving your car in second gear down the highway! I wonder why they designed it that way.

In the later Hartke model (HA3500) the voltage regulators in the power supply were replaced with a 15 volt versions (LM7815 & LM7915). In the later model they also increased the filter caps and installed them before the voltage regulator. In the earlier version (3500 MOSFET) they had filter caps before and after the voltage regulator.

[g1]

It's more like running your tires at 35psi cold when they are rated for max. 35psi cold. They can take more but that is the recommended upper range. And many manufacturers run them at the max. psi.
Another example would be a cap rated for 63 working volts being used at 63 volts. The manufacturer builds in some leeway, the cap doesn't explode at 64V.
The +/- 18 is the upper limit of the recommended range, they are not stressed if run that way. To get the full advantage of the chip, you would run at the upper safe limit. You will not get the same full signal headroom at a lower voltage. (although it is not always necessary, which is why they also used +/-15V in other variants)

As far as the caps after the regulators, they are probably required (see regulator spec sheet) but drawn elsewhere on the schematic, like this: