0
May 1997
AC power has many uses on the
bench. I am referring to some-
thing other than 120VAC.
Many things we repair need AC
power: Pac Man boards, some
Rock Ola amplifiers, motors, so-
lenoids, etc. Transformers pro-
vide these AC voltages. I
mounted some transformers on
a panel so I could add fuses,
power switches and indicator
lights. Useful voltages are 24 (or
48 with center tap), 18 or 20 cen-
ter tapped, 12, 6. An easy place
to get a selection of voltages at
fairly substantial current is an old
pinball transformer. Some older
(pre-switching supply) video
cabinets had big versatile trans-
formers too. The Williams De-
fender or Joust era cabinets and
the Taito cabinets come to mind.
Those particular transformers
and many others include a
120VAC isolation winding which
is handy on the bench. That
winding was for the monitor, so
if you are still using the cabinet
even though you replaced the
original supply with a switcher,
the transformer is still in use.
ythe
wayl
there is
absolutely
nothing wrong
with an old
Hnear supply,
either on your
bench or in a
game. Volts is
volts and amps
is amps.
@)@)
DMM
~
bench
meter
!7. I
Any data manual for linear ICs
that covers voltage regulators will
have simple circuit drawings for
variable regulator applications.
Just build their circuit. Try the
LM317 or something similar. If
you don't have everything in
your junk pile and you have to
buy parts such as metal case,
heatsink, transformers, etc. check
the surplus houses first. Though
it isn't necessary, a volt meter
right on the unit, and even a cur-
rent meter, is convenient, and
keeps your DMM free. Again,
panel meters are a heck of a lot
cheaper at surplus.
... continued on page 20
power
supply
1~0
(so you can get both + and -)
ranging 0-18 or 0-30 volts DC.
Commercial supplies cost hun-
dreds of dollars. This is a real
good place to build your own.
Since you can easily get 5 volts
elsewhere, just make the variable
sections. Unless you have spe-
cial needs,! would figure a 1 amp
supply to be sufficient power for
a variable supply.
Real handy is the standard bench
supply. It is usually a 5 volt sup-
ply and a pair of variable supplies
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