On 5 May 2007 04:32:02 -0700, Tim Shoppa
wrote:

William E. Sabin wrote:
"Computer Grade Capacitor" might possibly refer to the low value of internal
series resistance and inductance which are important parameters in switching
regulator power supplies.

Well, maybe "low inductance" by 1960's standards. A computer power
supply would have to filter 60Hz, or maybe 400Hz ripple then.

Apart from aviation, the last time the last time I heard someone using
400 Hz for powering computers was in the early 1960's with a 50/400 Hz
motor/generator in the basement, feeding the anode supply of some tube
computers :-), in order to reduce the transformer and filter capacity
size.

Yes,
there were switching supplies back in the 60's/70's too, but then
switching frequencies were much much lower (think about it: they used
2N3055's or their predecessors, transistors that take a millenium to
turn off!) than typical switching supplies today.

Outside TV EHT generators, primary switching power supplies were rare
in those days, simply because bipolars could not handle the rectified
mains voltage in those days, not at least with any significant
current, so linear power supplies was the norm in those days.

Clearly for their purposes, surplus 2N3055's and old big-can "computer
grade capacitors" can be put to very good use in many ham power
supplies. Make sure you get some LM723's too, a very versatile part
that modern parts (each good in their own narrow niche) have not
completely replaced yet!

My guess is that amateur radio is the last application in which linear
power supplies are used, since it is much easier to make a low noise
linear power supply than a switcher.

Paul OH3LWR