[Hallicrafters] Summary - SX-96/100 microphonics topic

[Mike Everette]

The contact-cleaning is VERY important.  If the bandswitch is full of "mung" this can, surprisingly, be a contributing factor.

When I worked in an avionics shop, we were constantly plagued with microphonic VHF Nav-Com transceivers, usually made by Narco.  For tuning, these radios employed "step inductors" which were similar to a rotary switch; the moving portion of the switch was the "coil."  The radios would become so microphonic that starting the engine in a Piper or Cessna would overwhelm the receiver completely.  Standard fix:  Use a white typewriter eraser (the pencil kind that must be sharpened) to clean the step inductor, followed by a GOOD contact cleaner like De-Oxit.  After that, tap the tubes with a wooden pencil to see if any of them were contributing to the problem; replace as necessary, clean ALL tube sockets and pins, tighten everything up, and an hour or so later it was ready to fly (maybe)... we tested every one on the ground in the plane with the engine fired up as a precaution; and flight tested any that we weren't sure about (if the aviator was willing to pay
 for it).

This stuff was old when I was working on it; and really made us ponder.  It seemed incredible what some people would trust their lives to....!  And there were a few even worse 20-year-newer radios buzzin' through the skies.

73

Mike
W4DSE