[Test-Equipment] Identify antique test gear

[Robert Nickels]

W0EOM at aol.com wrote:
>  I think it used tubes and batteries, with a  headset to hear the  'squeal'.
>   
My dad worked for a gas company and used to bring me the broken ones 
they used for locating pipes, which were made by a company called 
"Detectron".  This was in the mid-60s, and they all used miniature 
battery tubes and A and B batteries and headphones.   A few years agoI 
was telling him that I wish now I hadn't torn them all apart, and he dug 
around and found one for me .  It's transistorized and has a speaker but 
the same principle of operation is used.

73, Bob W9RAN