gil wrote:
Just got one of these "oldies" and my questions is...Why is this model
called the "AC-DC" version of the S-40?

Because its basically an AC-DC version of the S-40. That means it can
work either on Alternating Current (normal) or Direct Current (long gone
these days). In its era there were still areas that used 120 volts DC
instead of 120 volts AC.

And why is there no power transformer in this radio?

AC-DC radios don't use (can't use) a power transformer.

Without the power xfmr considerable cost was saved in production. In
this case some of the tubes are different and there is a ballast tube to
reduce the filament voltage. The filaments are wired in series (like
xmas tree lights) as opposed to parallel as in xfmr operated sets. The
B+ in the set runs at a lower voltage than a transformer operated set
since it takes voltage directly from the incoming AC (or DC) line and
rectifies it rather than stepping up via an xfmr.

There's no real problem in doing this, in fact its very common in
consumer electronics of the era. The main drawback in an older set is
that there may be (and likely will be) leakage in the old capacitors
that isolate the actual chassis from the neutral line inside the radio.
When leaky, one side of the AC line is essentially connected directly
to the chassis and this can pose a shock hazard so do be careful working
around the set.

Good luck,
Bill

See AC/DC sets at URL:
http://pw1.netcom.com/~wa2ise/radios/aa5h.html


"gil" wrote in message
...
Just got one of these "oldies" and my questions is...Why is this model
called the "AC-DC" version of the S-40?
And why is there no power transformer in this radio?

Any help or comments appreciated.

gil