S-100 power supply voltage ranges

[Roy J. Tellason]

On Monday 02 March 2009 01:15:19 pm Allison wrote:
> Some S100 chassis had multiple primary taps, CVT or a in the case of
> Inetgrand {and a few others} boxes regulators.
>
> The problem is the early machines had to have really robust transformers
> as the +8V bus could easily be 25A using early boards.  By 1980s with
> 64k ram cards (64k on one card) and multi serial IOs on one board a
> typical system might take from 3-5 board at far lower current than the
> earlier 4k ot 8k based memory systems.  The side effect fo that was the
> bus voltages being upregulated would float higher and regulators would
> run really hot.  Near the latter days typcail systems were system on a
> card (z80, 64k or even 128k, 2 serial, FDC and printer port) making the
> whole load typically under 3-4A at +8V and the need for more boards
> unlikely.

I also remember seeing boards that didn't have onboard regulators,  though 
there were positions for them.  Those contained wire jumpers,  and heatsinks 
were omitted,  the main PS having been replaced with a regulated switching 
PS...




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