I keep finding more goodies stashed away in my piles of stuff. Here's a Production Devices battery powered (two 9v) test oscillator with six fixed frequencies, variable gain, and switchable sine or square waveforms. Output connection is via banana jacks for you Serge people. Circuit is comprised of one opamp and five transistors. Lots of trimmers inside so I imagine you can vary those six fixed frequencies. Very clean but battery terminals have some light corrosion on them. Please see pics:
http://HOME1.GTE.NET/res05k5t/ebaypics/PD.jpghttp://HOME1.GTE.NET/res05k5t/ebaypics/PDinside.jpgProduction Devices primarily makes telcom test gear these days but they used to make some audio products. I have another one of their portable oscillators that I've had for years.
$35 gets this one to you including delivery anywhere within the continental USA.
I take PayPal, batteries not included, offer void where prohibited, etc.
Ivan