Hallo Wolfgang,

in the 80' we used TDA2003 lots of time for this task. For your purpose (80mA @ 35V) the following doubler or tripler could be used:



Switching frequency is about 4kHz. Keep in mind, that feedback from output is connected to non-inverting input. TDA2003 is not connected as linear amplifier, but as astable multivibrator!
With bigger electrolytics (1000µ) and diodes (1N5402) doubler can deliver up to 2A!! Also an inverter can be built with TDA2003...

When using these schemes for high output current, good cooling is essential! Circuits profit from TDA2003's SOAR protection of output transistors, from built-in thermal fuse, from absence of any inductor and from extremely low price of TDA2003 (about 1Euro)!

Viel Glück! (good luck!)

Kai