From: phil_a@tpg.com.au   
      
   **Hi,   
      
   my old valve Wien bridge oscillator has an interesting quirk.   
      
   During the warm up period, the frequency drops by a small amount.   
      
   About 6Hz at 2,000 or 34 Hz at 10,000 for a 10 degrees C rise.   
      
   So the tempco is negative, about 300ppm per degree C.   
      
   If I play hot air onto the MF resistors mounted on the range switch, the   
   frequency rises by a similar amount.   
      
   Has the ( 1940s) tuning gang got a significant negative tempco ?   
      
   Seems hard to believe,  given the very small coefficient of expansion of   
   aluminium and brass.   
      
      
   ....  Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)