[Lowfer] PA transistor getting hot - need advise

Andy - KU4XR ku4xr at yahoo.com
Fri Jul 25 23:24:35 EDT 2008


> Andy,
>  
> If you use the correct drive levels to your output
> 2222/2907 transistors and you are using a correct load the
> transistors will not get hot at the 1w output level. My
> circuit, that JA mentioned, has limiting diodes that help
> reduce the criticality of the base drive. 
>  

OK Everybody; This is for whoever wants to jump in with a 
comment on the " Base Drive Level ". How do I know what
" correct " is ??? I'm feeding the base of the PA transistors
from the 180 Ohm resistor. Is it possible that the 4017 chip
is " overdriving " the input to the PA ??? Would I be better
to put a Var. Pot. in place of the 180 Ohm and adjust for 
just enough drive level for stable oscillation ???

Also, to answer the question; I don't have a scope. Mine took
a lightning hit, and I can't afford to replace it at the moment.

This will be a useful learning experience for me and possibly 
many others, so, one issue at a time. Thanks to John Andrews,
I have come to understand that this PA is a switching type,
One transistor ON, the other OFF. Overlaps or Gaps are not what
we're looking for, and in my experimentation, I have saw 
firsthand what changing a component in the circuit will do. 
More on this in another post maybe.

Thanks for any input: 73, Andy - KU4XR


      


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