> >I was going to build an adjustable power supply with an output of 1.25 to 26
> >volts at 5 amps maximum. The transformers I ordered came in and the rectified
> >and filtered output is 39.5 volts and I had calculated for 28 volts.

The ripple and sag will easily bring it close to 28 volts, so you really
are where you want to be with 39.5 unloaded.

> >building two power supplies. I was wondering if a preregulator with a 2N3055
> >transistor, a 27 volt 1 watt zener diode and 1N4750A (27 volt, 1 watt, Izt =
> >9.5 mA nominal and 34 mA maximum) and a 1200 ohm half watt resistor (between
> >the collector and base) would drop the extra 11 volts I have?

You probably need more current to drive the 2n3055, it will likely have
fairly low gain at 5 amps.

I think the amount of heat you have to deal with will far overshadow these
small problems, however.

By the way, are you using a three-terminal adjustable regulator? It won't
work at the lower range of voltage with 28 volts in and 5 amps out. Too
much dissipation.

Perhaps five devices in parallel would work better.

Cheerful regards,

Bob

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