Recently, the model select knob on my Vax 600 will fall off if I turn the guitar upside down; to put on new strings, put in the batteries...   I changed strings yesterday and it fell off.  I put it back on, and was pretty sure it was on the guitar when I put it back in the bag.   I got to practice and didn't pay attention.  I turned it over to put in the battery pack and noticed it was gone when I turned it back over.   The damn thing was nowhere to be seen.   I checked everywhere around where I was sitting, and when I got home checked around where I had changed strings... nothing.   Is this available still, or am I out of luck?    I replaced it with an old submarine sonar knob I had from some scrap I brought home when I worked for the Navy.  It works pretty good, but now I know what the little leg on the bottom of the knob does.  The selector switch just continues to spin... the leg stops it.   Tonight should be interesting...