Hello James,

I need to generate 6v DC and 90v DC from a 12v DC automotive electrical
system to power an RT-70A/GRC surplus military radio. I need about 250 mA
at +6 volts and about 75 mA at +90 volts. I was thinking about using the
guts from an old battery back up but it would be a bit of a kluge. Are
there any 90 volt regulators in the 78xx series? How do I get the voltage
up to where I can get something that I can get the 90 volts from. ...

You can build a step-up or flyback with the LM3478. Tough to solder
though, it's a TSSOP package. Don't know what current you need but just
pick a suitable FET.

For 6V I'd use a buck regulator instead of wasting 50% of the energy in
a series regulator.

Regards, Joerg

http://www.analogconsultants.com