brings back a memory from the 50s.
There were many small sized communities in which telephone service
was provided by manual switchboards operated by independent
telephone companies. I was
employed by a telecom manufacturer
to convert these communities to dial
At one site, our customer (the
local phone company) had arranged
for Bell Systems to provide some
inter-connecting arrangements to
other exchanges. The installation of
their equipment was to be concurrent with ours. At one point, I was
asked where they could pick off 24
volts for their vacuum tube equipment. Our power source consisted of
23 lead-acid cells — 48 volts total. At
the direction of the TELCO engineer,
I tapped the battery midway and
created a distribution point on
I quickly found I could either boil
the water out of half the battery or let
the other half go flat. Perhaps the
engineer should have known better; I
certainly never suspected.
Fortunately, the 24 volt load was
quite steady. So, I mounted a number
of sockets on a piece of crating lumber and screwed in 100 watt light
bulbs until the loads were balanced —
I went on to another assignment,
but had an occasion to revisit the site
during an evening hour some
months later, only to find an eerie
glow of 115 volt bulbs still running
off the 24 volt bank. It was not the
kind of jury-rig I expected to remain
John S. Young
National Semiconductor has offered its
popular Webench online simulator for power
supply design for several years (see “Classic
Car Conversion” above). The company has
now broadened the scope of its online tools
with “Amplifiers Made Simple.” Use it to
design your next op-amp application.
Need to kill some time? Try this fun puzzle.
The Universe began not with a bang, but
with a low moan — building to a roar that
gave way to a deafening hiss. Hear it here.
Tired of waiting for Adobe’s Acrobat Reader
to load? The “Adobe Reader SpeedUp” is a
small utility that fixes that.
Circle #123 on the Reader Service Card.