Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdj!myers
From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: Re: Sine wave generator
Message-ID: <17660020@hpfcdj.HP.COM>
Date: 8 Sep 89 18:13:09 GMT
References: <24955@santra.UUCP>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 18

>Greg Bell writes:
>
>I'm going to all this trouble.  In addition, how do the sine wave generators
>that use the PTC of a particular light bulb work???                          
>
>The light bulb's non-linear resistance is (hopefully) used to
>control the amplitude of the oscillation to keep the amp in
>it's linear region (necessary for good sines). Messers Hewlett
>and Packard made a bunch of money off that kind of oscillator!

Specifically, find a good reference to the "Wien-bridge" oscillator circuit;
the bulb is used as one of the resistances in the resistive-divider side of 
the bridge, and so provides "automatic" amplitude adjustment.


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.