Re: longitudinal waves

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "rheidlebaugh by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
> 
> Dave: I suspect I am just a bit older than you, 50+ years or so. I think I
> should let you know that modern speakers are low impedance and will not work
> on a crystal set. You will nead to make your own high impedance speakers
> 2-20k as they are no longer made. Even high impedance ear phones are hard to
> get except surplus. You might try a crystal transducer or use an amplifier.
>   Robert  H

	Fair Radio Sales has surplus high-impedance headphones for sale at
fairly reasonable prices, and some of the antique radio supply houses
have good old headphones for around ten to fifteen bucks.  However, with
a single LM324 opamp, available for peanuts, you can build a high-gain
audio amp which will drive any of the modern 8 ohm earphones quite
nicely, using a 9V transistor radio battery for the power.  I have one
here which I built while playing with high-performance crystal
receivers.  Has selectable gains of 10, 100, 1000, and 10000.  One
afternoon's project and a generally useful little gadget.

Ed