[TenTec] Two Century 21 problems

[Tom NØJMY]

I'm going back together with the first of four Century 21's here.  First 
off, is it me, or are the set screws in the main tuning knobs really 
tiny?  Such that the threads in the knob are excruciatingly fragile?  I 
haven't got one out of the four that will tighten enough to stay secured 
to the PTO shaft.  A couple of the screws can be pushed right through. 
Any thoughts on a simple fix for my simple mind?

Second, and more serious.  I had one up and running yesterday on 20 
meters.  Seemed to have good sensitivity, maybe even above average.  So 
I plugged in the matching calibrator which put in a deafening 
signal...for awhile.  As I tuned to zero-beat the audio quit completely.

After monkeying around with it for about twenty minutes without plan, I 
switched the selectivity control from narrow to the middle position and 
pop, the audio came back.  On all three bandwidths.

So I turned the RF and AF controls way down, turned the calibrator back 
on and started increasing the gain.  Like an idiot, I can't remember 
which one, maybe both - arrgh!  The calibrator had plenty of signal all 
the way to the top of ten meters.

But as I continued to increase gain, poof.  No audio again.  It wasn't 
near maximum gain either.  And this time it hasn't come back.

What would cause this behavior?  And any ideas where I should start my 
trouble-shooting?  Being primarily a boat-anchor man, I can use all the 
help I can get.

Thanks,
Tom