[Boatanchors] [ARC5] BC-375: STABLE AM QSO on 7160 KC

[Dennis DuVall]

All,

Maybe time for a couple of reality checks here.  First, has anyone  
duplicated David's results and beyond that, checked the results with  
different chokes as discussed by Arden.
Trying different brands of oscillator tubes might give some  
interesting data points as well.  I have a pair of Amprex 211s which  
have considerably different internal construction
than the usual VT-4C. Will plug one into the oscillator socket on my  
-375 and report back.  Also, there should be some way to get cooling  
air flowing around the suspect
components in the TU and observing what results that might have.

Like others, I had long assumed that the frequency shift observed in  
these radios on key down, negligible on 160, slight nuisance on 75/80  
and definitely a problem on 40,
was a consequence of geometric changes that came with  heating up that  
massive plate structure in the oscillator tube.  The time constant  
seemed to be about right too.
I have mused from time to time about schemes to keep the plate current  
flowing through the oscillator tube continuously while, at the same  
tome,  quenching the oscillations
on key-up by some other means.   Never came up with an easy way to do  
it though.....  :^(

Dennis D, W7QHO
Glendale, CA