"David" wrote in message
...
Looking for Crystal Radio Receiver Circuits, that have a voltage
quadrupler to increase headphone volume without batteries or AC power.

Hi David,
I don't think it really works that way. The audio is level is dependent on
the level of the RF signal.
Get a long antenna and sensitive headphones.
Check the http://members.shaw.ca/ve7sl/crystal.html
and see the list at the bottom, check out Rap N Tap.
Mike