On Mon, 29 May 2006 11:14:26 -0300, "jtaylor"
wrote:

When I was little(r), almost all small portable radios used 9-volt
batteries. There were some, of course, that used AA's (or even 1 AA; I had
an am portable with 1 AA cell that we snuck into school when
something-or-other REALLY important to schoolboys was going on), but now I
don't have & don't know of any radio that uses 9V batteries.

Why were they needed in the first place? The 9-volt package has a lot more
package and a lot less mWatthrs in it. Was it because of the voltage - did
the existing solid-state tech not work so well at 3V?

Mostly history and technology. The first transistors were germanium
point junction transistors. Germanium transistors has lower charge
carrier mobility than Silicon, and higher voltage losses across the
junction than Silicon. To get significant power, and gain, these
devices needed much higher voltages. 9 Volts also allowed
manufacturers to save some money. The speaker could be connected
directly to the output stage (no transformer), something that is hard
to do with 3 volts and a class B output stage. 9 volts is the norm for
these devices into the 1970's. So almost anything you see from the
1950's and 1960's uses 9 volts.