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. Getting
the 6 volts doesn't seem to be a problem. A 7806 off the battery should
work for that unless any of you can see a problem doing that. [ Maybe the
common common would be a problem. Right now I'm running it off of an HP6299A
and an HP6236B with commons jumpered. I'd like to be able to go portable
with it. ]



90V @70ma is only 6.3W and a step-up of no more than 90/12=7.5. This
would be something like a 24VAC center-tapped transformer turned
backwards with a multivibrator drive of the secondary at 50-60Hz and the
usual primary is rectified and capacitor filtered to produce the 90V.
Since the reflected current is only about 1/2A, you can then feedback
the rectified HV to drive an error amp that regulates the center tap
down to 9V or so.